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SingularityHRT3

Second Lieutenant
Sep 1, 2020
101
217
Information in this Post could be Obsolete for any version over 1.0.3

Before We dive into Succession Laws, BASICS.
{Correct Me if any information given is wrong. If You disagree with any information given, be respectful and I am open for a healthy argument. Feel free to give any suggestion to improve this Thread}

Player Heir: The character the Player (You) will continue to play in the game if the current character that You are playing dies. Player Heir can only be of the character’s Dynasty. Usually, it is the Eldest Child of the Ruler who is the Player Heir (unless the Succession Law states otherwise).

Primary Heir: The character who will inherit the Primary Title of the Ruler when the Ruler dies.
{The Player Heir might be different from the Primary Heir in some Succession Laws, especially in Elective type laws, where the Primary Heir can be someone from another Dynasty.}

Eligible Child: Children of the Ruler who are allowed to inherit based on Gender Law. Bastards can stand to inherit only if they are legitimized (Marriage Doctrine under Faith dictates if Bastards can be legitimized).
Male Only: Only the Son(s) of the Ruler (including Bastards if legitimized) are Eligible Children for inheritance. The Daughter(s) of the Ruler are not eligible for inheritance, even if the Ruler doesn't have a Son.​
{If a Ruler has 3 Sons and 2 Daughters, only those 3 Sons can inherit the Ruler’s Titles. If the Ruler has no Son and 2 Daughters, the Daughters will never inherit.}
Male Preference: The Daughter(s) of the Ruler (including Bastards if legitimized) are Eligible Children for inheritance if and only if the Ruler has no Son. If the Ruler has even one Son, the Daughter(s) will not be eligible for inheritance.​
{If a Ruler has 3 Sons and 2 Daughters, only those 3 Sons can inherit the Ruler’s Titles. If the Ruler has no Sons and 2 Daughters, the Daughters can inherit}
Equal: Every Child of the Ruler (including Bastards if legitimized) are eligible for inheritance.​
{If a Ruler has 3 Sons and 2 Daughters, all of them can inherit the Ruler’s Titles. If the Ruler has no Son and 2 Daughters, the Daughters can inherit}
Female Only and Female Preference are the same as Male Only and Male Preference but the genders are flipped.​
Screenshot_11.png

Claims:
Implicit Claim: All Children of the Ruler have an implicit claim on all Ruler's Titles until the Ruler dies.​
{For some reason, no matter the Gender Law, Daughters don't seem to have any Implicit Claim}
Pressed Claim: Each Child of the Ruler gets a pressed claim on all Titles of the Ruler that they don't inherit (or is not in their Realm) when the Ruler dies.​

Title Tier: Empire > Kingdom > Duchy > County > Barony
Might have a different name for different religions and/or governments but the tier will be the same.

The Line of Succession: The order in which the Eligible Children (or Candidates) "stand to inherit" Titles of the Ruler. In most cases, The eldest Eligible Child is the 1st in the Line of Succession and the youngest Eligible Child is the Last in the Line of Succession.
For Ultimogeniture The order is reversed and for House Seniority, it starts with the eldest Living Member of the Player's House to the youngest.

NOTE 1: You can not grant a Titles to You Primary Heir which some other Eligible Child stands to inherit. But You can grant a Title that Your Primary Heir stands to inherit to the other Eligible Children.
NOTE 2: Baronies of the Ruler will be inherited by the Eligible Child who will inherits the County that it belongs to.



Succession Laws
Rules according to which the Titles of the Ruler are inherited by the Eligible Children on the Ruler’s death. These laws only apply to Eligible Children of the Ruler.​
There are 2 different places where the Succession Laws apply.
One is Realm Succession Law, which dictates how all the Titles held by the Ruler will be inherited by the Eligible Child (or House Member in case of House Seniority). In Realm Succession Law, only members of your House will be eligible to inherit.
Another is Title Succession Law for every higher tier Title starting from the Duchy tier. Title Succession Law will apply to each individual Title after the Realm Succession Laws are applied.


Realm Succession Law:
Applies to the Realm as a whole.
Screenshot_12.png
Multiple Heir Succession,

“Order of the Titles”: This is a term that I will use to state the order in which the Titles of the different tier will be arranged for inheritance. The character details (the one that shows the details of a character including Titles held when You click on a character) will have Titles held by them in a specific order.​
The order is, as far as I can understand,​
1. Primary Title will be the first in order.​
2. Higher tier Titles are ordered before (to the left of) the lower tier Titles.​
3. For the Titles of the Same tier, the older Titles (the Titles that were inherited or created or usurped by the Ruler before the others) is ordered before (to the left of) newer Titles.​
{Eg: A King has 5 Kingdoms, 2 Duchies and 5 Counts.
He inherited 2 Kingdoms K1 and K2, then usurped Kingdom K3, then created Kingdom K4, then destroyed and recreated Kingdom K2, and then inherited Kingdom K5 and made it the Primary Title.
He has enough De Jure Counties to form 3 Kingdoms of which K6x has the highest number of De Jure Titles under it held by the King followed by K7x and then K8x (initial testing shows that the order is based on number of De Jure Titles under it held, I could be wrong and the primary factor could be something else).
Duchy D1 was inherited and Duchy D2, the De Jure Duchy of the Realm Capital, was created later.
The 5 Counties He inherited are C1, C2 and C3, followed by taking C4 and C5 in a war and then made C4 the Realm Capital.
The order in which all these Titles will be displayed in the character details will be (from left to right)
K5 K1 K3 K4 K2 D1 D2 D3 C1 C2 C3 C4 C5
The order in which it will be inherited is
K5 K1 K3 K4 K2 K6x K7x K8x D1 D2 D3 C1 C2 C3 C4 C5}
"Order of Distribution": This is a term I will use to state how the remaining Titles of the "same tier" will be inherited by the "remaining" Eligible Children once the Ruler dies in Multiple Heir Succession type Succession Laws. I stress the word "remaining" as Titles that are inherited before (or higher tier Titles) will not be available for inheritance and Eligible Children who have already inherited higher tier Titles will become ineligible for inheritance in lower tier Titles (except Primary Heir).​
Step 1: Only Eligible Children with "0"(zero/no) Title of equal or higher tier within that realm will be a participant of Round "1".​
Step 2: For all the Participant in Round "1", each one based on the Line of Succession will inherit one Title of that tier following the "Order of the Title". Round "1" ends.​
Step 3: If there are Titles of that tier left, only Eligible Children with "1" Title of equal or higher tier within that realm will be a participant of Round "2".​
Step 4: For all the Participant in Round "2", each one based on the Line of Succession will inherit one Title of that tier following the "Order of the Title". Round "2" ends.​
The same pattern will be followed until all Titles of that tier are inherited.​
Note 1: If an Eligible Child already held Title(s) of that tier when the Succession happens, that Title will also be included in the count to determine eligibility for every Round.​
Note 2: Primary Heir who might inherit De Jure Titles of the Realm Capital before "Order of Distribution" is applied, will also have that De Jure Title of that tier included in the count to determine eligibility for every Round.​
{Eg: A King has a Kingdom K and 7 Duchies D1 to D6 in the "Order of the Titles" and DJ the De Jure Duchy of the Realm Capital.
He has 3 Eligible Child PH, H1 and H2 in the order of the Line of Succession. PH is the Primary Heir.
PH and H2 hold a Duchy each (D1x and D2x respectively) when the King is alive.
When the King dies, Succession fires under Confederate Partition law.
PH will inherit K, the Primary Title, and DJ the De Jure Duchy of the Realm Capital.
Round 1 for Duchy: PH with 2 Duchies and a Kingdom (D1x, DJ and K) and H2 with 1 Duchy (D2x) can not participate. Only H1 with 0 Duchy of higher tier can participate. H1 gets D1.
Round 2 for Duchy: PH with 3 equal or higher tier Titles can not participate while H1 with D1 and H2 with D2x can participate, each having only 1. H1, being higher in the Line of Succession, will get D2 and then H2 will get D3.
Round 3 for Duchy: PH has 3 equal or higher tier Title (D1x, DJ and K) while H1 and H2 have only 2. So H1 gets D4 and H2 gets D5
Round 3 for Duchy: Everyone is eligible as all have 3 equal or higher tier Titles. PH starts with D6 and H1 get D7. Round ends as no more Titles are left.
PH has K, D1x, DJ, and D6. H1 has D1, D2 D4 and D7. H2 has D2x, D3 and D5.}

1. Confederate Partition:​
{“#TheMostConfusingPartitonEverInHistory” for almost everyone new Player. Some argue that this type of Partition is ahistorical only because they don’t understand it well. I would recommend playing in debug mode to explore how Succession Law works for different kinds of setups (that is how I learned). Once You understand the Confederate Partition, every other Succession Laws will be easier to understand as they are just simplified versions of the former. I will include an example after explaining all the rules so do read till the end and compare the example with the rules below. Example under construction.}
Rule:​
Eligible Children will only inherit Titles held by the Ruler (new Titles of the Primary Title tier will be created if enough De Jure Counties under it is held, but Titles will not be usurped).​
If an Eligible Child is to inherit a Duchy or higher Title without being landed or having any County to inherit under it, the De Jure Capital County of the highest tier Title inherited will be automatically given to the Child if it is present in the Realm. If the De Jure Capital of the highest tier Title is outside the Realm, the De Jure Capital of a Title below the highest tier Title will be given.​
Step 1:​
Primary Heir (usually the Player Heir) will inherit the Primary Title, the Realm Capital (Realm Capital can be changed once per Ruler) and all lower tier De Jure Titles the Realm Capital belongs to (De Jure Duchy of the Realm Capital if the Ruler is a King, also the De Jure Kingdom of that Duchy if the Ruler is an Emperor).​
No new Title will be created in this step.​
Step 2:​
Titles of the same tier as the Primary Title will be created if it can be (if the Ruler holds enough De Jure Counties under that Title).​
Titles of that tier will be inherited based on the "Order of Distribution" by all the Eligible Children including the Primary Heir. If the Realm Capital is De Jure County of a Title (of the same tier as the Primary Title) other than the Primary Title, Primary Heir will inherit that if He stands to inherit more than two Titles of the Primary Title tier (in this step).​
All Titles of lower tier that are De Jure of the inherited Titles will be inherited by the respective Children.​
Every Eligible Child that inherits a Title in this step will become independent.​
Every Eligible Child, except the Primary Heir, that inherits a Title in this step will not stand to inherit any Titles of low tier (i.e., will not be a part of the following steps).​
Step 3:​
If there are no Eligible Child left for the remaining Titles, The Primary Heir inherits all the remaining Titles. If there is even one Eligible Child other than the Primary Heir left to inherit a Title, the next step is followed.​
Step 4:​
Titles, one tier below the last inherited tier of Titles, will be inherited based on the "Order of Distribution" by all the remaining Eligible Children including the Primary Heir.​
All Titles of lower tier that are De Jure of the inherited Titles will be inherited by the respective Children.​
Every Eligible Child that inherits a Title in this step will become the Vassal of the Primary Heir.​
Every Eligible Child, except the Primary Heir, that inherits a Title in this step will not stand to inherit any Titles of low tier.​
Step 5:​
Last two steps are repeated until all Titles are inherited.​

2. Partition:​
Same as Confederate Partition but no new Titles will be created in any Step 2.​
3. High Partition:​
Step 1 of Confederate Partition.​
Step 2 of Confederate Partition.​
Step 3:​
Primary Heir will inherit the lion’s share (as much as possible but not more than 50%) of the Titles on the same tier of the Primary Title, the oldest Titles held by the Ruler will be prioritized. Lion’s share for the Primary Heir (includes the De Jure Title of the Realm Capital given in the previous step). If the Realm Capital is De Jure County of a Title (of the same tier as the Primary Title) other than the Primary Title, Primary Heir will inherit that if He stands to inherit more than two Titles of the Primary Title tier (in this step).​
The remaining Titles of the same tier will be inherited based on the “Order of Distribution” by the remaining Eligible Children except the Primary Heir.​
All Titles of lower tier that are De Jure of the inherited Titles will be inherited by the respective Children.​
Every Eligible Child that inherits a Title in this step will become independent.​
Every Eligible Child, except the Primary Heir, that inherits a Title in this step will not stand to inherit any Titles of low tier (i.e., will not be a part of the following steps).​
Step 4:​
Each subsequent lower tier Title follows the same rule as the previous step where the Primary Heir will get the lion’s share of the remaining Titles of that tier (including De Jure Title of the Realm Capital).​
The remaining Titles of the same tier will be inherited based on the “Order of Distribution” by the remaining Eligible Children except the Primary Heir.​
All Titles of lower tier that are De Jure of the inherited Titles will be inherited by the respective Children.​
Every Eligible Child that inherits a Title in this step will become the Vassal of the Primary Heir.​
Every Eligible Child, except the Primary Heir, that inherits a Title in this step will not stand to inherit any Titles of low tier.​
Step 5:
The previous step of lion's share inheritance by the Primary Heir followed by “Order of Distribution” for the remaining Eligible Children continues until all remaining Titles including Counties (if enough Eligible Children are present) will be inherited.​

Single Heir Succession,

1. Primogeniture:​
The Oldest Eligible Child will inherit all Titles. Other Eligible Children will inherit no Title.​
2. Ultimogeniture:​
The Youngest Eligible Child will inherit all Titles. Other Eligible Children will inherit no Title.​
3. House Seniority:​
Oldest living member of the Player’s House will inherit all Titles. If that oldest member is not an Eligible Child, none of the Eligible Children will inherit any Title.​


Title Succession Law:
Laws that applies to individual Titles after Realm Succession Laws are applied. Can be viewed and changed in the Title screen that appears when the banner of the Title is selected.
Screenshot_13.png

There are 6 different types, which are,

1. Same Realm Succession Law but with a different Gender Preference for the Title.​
This law will be applied alongside Realm Succession Law. The Realm Succession Law can have male preference but if a Title has female preference, the succession will be different.​
2. Feudal Elective:​
Electors: Ruler, De Jure Vassals of upto two ranks/tier below the Title.​
Nominees: Close Family of Ruler, De Jure Vassals of upto two ranks/tier below the Title.​
3. Princely Elective:​
Electors: Emperor, the seven Prince-Electors.​
Nominees: Ruler’s Legitimate Children and Siblings, the seven Prince-Electors, major De Jure Vassals of the Empire.​
4. Saxon Elective:​
Electors: Ruler, all direct adult De Jure Vassals of upto two ranks/tier below the Title.​
Nominees: Ruler’s Legitimate Children, Powerful Vassals, Claimants.​
5. Scandinavian Elective:​
Electors: Ruler, all De Jure Vassals except Barons.​
Nominees: Ruler’s extended Family, Claimants​
6. Tanistry Elective:​
Electors: Ruler, all Vassal upto two ranks/tier below the Title.​
Nominees: Ruler’s Dynasty members.​

{In certain conditions, the Primary Heir might be the successor according to Realm Succession Law but because of the Title Succession Law, he might lose that Title to someone else in Elections, even to someone outside the Player’s Dynasty.}
WARNING! At the current state of the Game, a different Title Succession Law seems to break the Succession Mechanic. I am still sure if it is working as intended (and Me unable to understand) or the Mechanic is indeed broken. I would suggest You not to change the Title succession law just to make sure You game plans work the way You want to.

A Save Game to demonstrate all these Succession Laws is being prepared. I will add it soon, so do check later.
 
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Honestly, realizing that you keep the entire du jure title one level below your primary makes me like the system quite a bit more. My first ruler was only a duke, and it was horrifying to see him lose just about everything in his capital duchy. But subsequently I've had kings, and as long as you have a powerful duchy it's not bad losing stuff outside of it.

Thanks for the write-up!
 
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Honestly, realizing that you keep the entire du jure title one level below your primary makes me like the system quite a bit more. My first ruler was only a duke, and it was horrifying to see him lose just about everything in his capital duchy. But subsequently I've had kings, and as long as you have a powerful duchy it's not bad losing stuff outside of it.

Thanks for the write-up!
Even if You are an Emperor, You can lose every county in You Capital Duchy if You have enough Eligible Children. Best way to save it from happening is to have equal or more number of Duchy or higher tier Titles than the number of Eligible Children.
Eg; An Emperor has 3 Kingdom Titles (including De Jure Kingdom of the Realm Capital) and 2 Duchy Titles (including Capital Duchy) and all Counties in the Capital Duchy. For Partition Succession or Confederate Partition Succession,
If there are 4 (or less) Eligible Children, 2 will get one Kingdom each and the youngest will take the other Duchy. All Counties will be inherited by the Player Heir.
If there are more than 4 Eligible Children, each Child younger than the 4th will inherit one County even if it is under the Capital Duchy of the Player Heir. Sometimes all but the Realm Capital will be the only county left for the Player Heir.
 
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one of the things that mad sucks is there doesnt seem to be a way to make your elected heir inherit everything

first thing i do in any crusader kings campaign is rush down literally any form of elective succession so i can freely pick out my heir if my eldest son turns out garbage. theres no way to sort out a single heir elective succession in ck3 though, partition will grant all your sons a bunch of counties and the single heir successions will hand all the counties of your primary duchy to whomever would typically inherit under regular single heir succession

honestly its kinda hard to tell if its wad or not, i wanna get my really good third son on the throne but im gonna have to immediately kick off his reign trying to get all my counties back from my eldest son, and that seems kind of like an oversight
 
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Two notes - it's arguable whether those behaviours are WAD, I'd rather go with not:

1) at the moment it looks like the gender preference title laws exclude the title from being counted during partition, which causes titles not to get split:

2) princely elective however seems to count for confederate partition making HRE spit out random Italias:
 
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one of the things that mad sucks is there doesnt seem to be a way to make your elected heir inherit everything

first thing i do in any crusader kings campaign is rush down literally any form of elective succession so i can freely pick out my heir if my eldest son turns out garbage. theres no way to sort out a single heir elective succession in ck3 though, partition will grant all your sons a bunch of counties and the single heir successions will hand all the counties of your primary duchy to whomever would typically inherit under regular single heir succession

honestly its kinda hard to tell if its wad or not, i wanna get my really good third son on the throne but im gonna have to immediately kick off his reign trying to get all my counties back from my eldest son, and that seems kind of like an oversight
Two notes - it's arguable whether those behaviours are WAD, I'd rather go with not:

1) at the moment it looks like the gender preference title laws exclude the title from being counted during partition, which causes titles not to get split:

2) princely elective however seems to count for confederate partition making HRE spit out random Italias:
There seems to be "Calculation mistake" in the logic of how succession should be handled for different titles successions. So having a "Male only" succession in a confederate partition of male preference and HRE seems to be broken.
 
one of the things that mad sucks is there doesnt seem to be a way to make your elected heir inherit everything

first thing i do in any crusader kings campaign is rush down literally any form of elective succession so i can freely pick out my heir if my eldest son turns out garbage. theres no way to sort out a single heir elective succession in ck3 though, partition will grant all your sons a bunch of counties and the single heir successions will hand all the counties of your primary duchy to whomever would typically inherit under regular single heir succession

honestly its kinda hard to tell if its wad or not, i wanna get my really good third son on the throne but im gonna have to immediately kick off his reign trying to get all my counties back from my eldest son, and that seems kind of like an oversight
There is one way, disinherit the male heirs other than him (before they breed).
 
WARNING! At the current state of the Game, a different Title Succession Law seems to break the Succession Mechanic. I am still sure if it is working as intended (and Me unable to understand) or the Mechanic is indeed broken. I would suggest You not to change the Title succession law just to make sure You game plans work the way You want to.
 
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At the current state of the Game, a different Title Succession Law seems to break the Succession Mechanic. I am still sure if it is working as intended (and Me unable to understand) or the Mechanic is indeed broken
We had it declared that capital and house head status should stay under player's heir control. They quite often doesn't. Therefore, not WAD.
 
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Isn't Confederate Partition the only one that is supposed to create new titles? I switched to High Partition but in-game it is still trying to tell me that the second son is going to get a Kingdom that I haven't created.
 
Isn't Confederate Partition the only one that is supposed to create new titles? I switched to High Partition but in-game it is still trying to tell me that the second son is going to get a Kingdom that I haven't created.

I had the same when I switched from Confederate Partition to Partition earlier today. In the end it was only a visual bug when I hovered over a character. If you go into the succession menu the title should not be listed there.
 
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Yea, I sort of accidently figured out how Confederate Partition worked when I was trying to figure out why the Duchy of Kiev (has special inheritance rules) was being displayed outside of the normal succession rules inside the Realm tab.

Just a note, it might be a bug, but titles with special inheritance rules seem to mess up the order of titles and the general inheritance. Quick rundown of what this "bug" seemed to be doing. I had 3 kingdoms, 2 duchies, 6 counties. I had 2 sons. With Duchy of Kiev having special rules, it was excluded from the normal succession break down in the Realm tab. My primary heir was still getting the title, but, it was impacting the overall succession. In the realm tab succession section my heir was getting primary kingdom, + smallest kingdom, and a single county inside the Duchy of Kiev. The duchy of Kiev was granted separately. My second son was getting K of White Rus', Duchy of Minsk, 2 counties inside Minsk, and all the remaining counties in Kiev, for a total of 5 counties, and a total of 8 titles lost. My heir was getting 4 titles and ONE landed title.

I removed the special inheritance rule for D of Kiev, and the entire thing snapped into shape the way you laid it out. My primary heir inherited everything inside K of Ruthenia. My secondary heir got everything inside K of White Rus, when a third boy was born, he was slated to get Galicia-Volhynia, no duchies, and a single county from Kiev.

So it seems that titles with special inheritance rules that differ from the rest of the realm can fog the entire thing up.
 
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Let me leave it here:

 
Yea, I sort of accidently figured out how Confederate Partition worked when I was trying to figure out why the Duchy of Kiev (has special inheritance rules) was being displayed outside of the normal succession rules inside the Realm tab.

Just a note, it might be a bug, but titles with special inheritance rules seem to mess up the order of titles and the general inheritance. Quick rundown of what this "bug" seemed to be doing. I had 3 kingdoms, 2 duchies, 6 counties. I had 2 sons. With Duchy of Kiev having special rules, it was excluded from the normal succession break down in the Realm tab. My primary heir was still getting the title, but, it was impacting the overall succession. In the realm tab succession section my heir was getting primary kingdom, + smallest kingdom, and a single county inside the Duchy of Kiev. The duchy of Kiev was granted separately. My second son was getting K of White Rus', Duchy of Minsk, 2 counties inside Minsk, and all the remaining counties in Kiev, for a total of 5 counties, and a total of 8 titles lost. My heir was getting 4 titles and ONE landed title.

I removed the special inheritance rule for D of Kiev, and the entire thing snapped into shape the way you laid it out. My primary heir inherited everything inside K of Ruthenia. My secondary heir got everything inside K of White Rus, when a third boy was born, he was slated to get Galicia-Volhynia, no duchies, and a single county from Kiev.

So it seems that titles with special inheritance rules that differ from the rest of the realm can fog the entire thing up.
Yes indeed. When I tested the rules, I tried it in debug mode. Everything worked perfectly as per rules until I started changing the Title Succession Laws. I tried to dig into game files to understand it but as I am new to game rules in files I couldn't find the exact file/rule there. Simple logic changes can fix these issues. I hope Paradox does that sooner than later before any other fix.
 
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“Order of the Titles”: This is a term that I will use to state the order in which the Titles of the same tier will be inherited by multiple Heirs. The character details (the one that shows the details of a character including Titles held when You click on a character) will have Titles held by them in a specific order. As far as I can understand, the Titles will be ordered such that the higher tire Titles are ordered before lower tier Titles, Primary Title is listed first and the next Titles will be in order such that the Title the Ruler acquired the earliest (oldest) either by inheritance or creation or by usurping is listed before the newer Titles. During succession, for the same tier Titles, the Primary Title or the De Jure Title of the Realm Capital will be inherited by the Primary Heir and each further Titles will be inherited by the next oldest Son in order of rotation in such a manner that at any point of distribution, except for the first round of rotation, the Primary Heir doesn’t have more Titles of the same tier than his Siblings left eligible for succession.
{Eg:
Ruler has 7 Duchy Titles namely A, B, C, D, E, F and P where P is the Primary Title while others are in order from oldest to newest Title.
He has 3 Eligible Children X, Y and Z where X is the Primary Heir and Z the youngest.
On A’s death, X will get P, then Y will get A, Z takes B in the first round.
The second round starts with Y taking C since if X is given C, he will have more Titles of the same tier than all his siblings having at least 1 Title of that tier. Z takes D and X takes E
Third round will have Y taking F. All Titles of the Duchy tier are inherited so round ends.}
Simply put, the first round will start with the Primary Heir and the oldest Child getting the Primary Title and ending with the youngest Child. From second round onward, the 2nd oldest will start and the Primary Heir will end after the youngest Child.

NOTE: You can not grant a Titles to You Eligible Child which some other Eligible Child stands to inherit.

So Primary heir gets duchies P, E (2 duchies);
Second son gets A, C, F (3 duchies);
Third son gets Y, D (2 duchies).

That means that when you have more titles of the same rank than you have eligible children, your heir's siblings will always get the same amount of titles or better.

Shouldn't the heir always end up with the best deal?
 
So Primary heir gets duchies P, E (2 duchies);
Second son gets A, C, F (3 duchies);
Third son gets Y, D (2 duchies).

That means that when you have more titles of the same rank than you have eligible children, your heir's siblings will always get the same amount of titles or better.

Shouldn't the heir always end up with the best deal?
It doesn't always work that way for Confederate Partition (and Partition). Younger Heirs are given more priority to get titles than the Primary Heir. In certain scenarios, only the Primary Title, Realm Capital and it's De Jure higher tier Titles while the next Heir might get twice that many Titles and more Holdings. In another Scenario, The Primary Heir might get all Titles and Holdings leaving only a Duchy Title for the next Heir.
Primary Heir will get the Best deal from Higher Partition and above.
 
It doesn't always work that way for Confederate Partition (and Partition). Younger Heirs are given more priority to get titles than the Primary Heir. In certain scenarios, only the Primary Title, Realm Capital and it's De Jure higher tier Titles while the next Heir might get twice that many Titles and more Holdings. In another Scenario, The Primary Heir might get all Titles and Holdings leaving only a Duchy Title for the next Heir.
Primary Heir will get the Best deal from Higher Partition and above.

But even in lower partition types your primary heir should get the best deal. Let's go with a simple example, 2 sons, 3 duchies. By the current logic, the second son gets 2 duchies, while your heir only gets one.