From the below Airforce Strategy guide link on the HOI Wiki it advises primarily for Interceptors/Multi-Role Fighters under
Stack Size;
http://www.paradoxian.org/hoi3wiki/Airforce_strategy
“Every wing beyond the first incurs a significant stacking penalty. Due to this penalty, the most efficient stack size is simply one wing of aircraft (representing 100 fighters). Due to the stacking penalty, you do not want to have super-stacks flying around. The stacking penalty is 10% for every wing above the first one. The most effective stack size though cannot be told beforehand, as the optimum shifts towards higher stack sizes the more bonuses you get from technology, experience and leaders.
Examples: With 0% additional bonuses from tech/experience/leaders, the stack size that packs the most punch is five or six wings, with 30% bonuses it becomes seven wings and with 50% it becomes eight wings. For further details confer Air_combat_reference. [
http://www.paradoxian.org/hoi3wiki/Stacking_penalty#Stacking_Penalty]
Since you normally want a compromise between efficiency and effectiveness, you would settle for stack sizes between four and six planes.
Also be aware of the air leader command limits, which are 4/8/12/16. So usually the two lowest ranks are absolutely sufficient, but as soon as two groups operate in the same area and may end in the same air battle one of the two air leaders should be promoted accordingly, if this situation is to occur more often. Higher ranks are nearly useless as there is no reason for a player to have those huge stacks with those huge penalties.”
However despite what this says I don’t think the optimal number really changes since it is the same 10% Penalty per extra squadron, so the ratio difference between the various numbers doesn’t really change even though as the bonuses accrue and increase the total benefit to all stack sizes it just means the effectiveness of each stack size improves at a similar rate. The ratio difference doesn’t change no matter how many positive bonuses are employed, the effective efficiency ratio changes between the different sizes is going to remain the same.
Well that looks simple but as we know the bonuses and other penalties affect final strength points of both attack and defence, especially for INT/MRF on either Interception or Air Superiority Missions in Air-to-Air combat because they instantly obtain a 20% attack bonus, but it isn’t applied to their defence.
Also the way that the whole sum of penalties and bonuses are applied to produce the actual efficiency modifier isn’t simple, have a look at the bottom of the Air Stacking Penalty Wiki, see here:
http://www.paradoxian.org/hoi3wiki/Stacking_penalty#Stacking_Penalty
So it goes like this, the base value is increased by the experience bonus and then that result (for instance at 30% experience is 1.3) is then increased by the Interception bonus of 20% (so 1.3 times 1.2 = 1.56) then the Mission efficiency value of your TECH advance in this at 5% per level is applied followed by the 10% radio bonus is applied (1.56 times 1.1 = 1.716) other bonuses such as 10% base proximity, Night Flyer trait & Axis territorial pride and penalties such as Weather and Night difficulty are applied next somewhere in order I think then the Stacking Penalty is applied second last reducing the variable rate of everything else above it in the order, then finally the Leadership Modifier is applied.
The way this works is important because all those other bonuses – penalty result is reduced by the Stacking Penalty just before the Leadership skill bonus at 5% per skill point modifier is applied. This means that an extra skill point Leader has proportionally greater benefit than a similar percentage bonus in other areas before they are reduced by the Stacking Penalty modifier. So an extra point of skill at 5% is worth more than an extra level of Mission efficiency also at 5%. Similarly 2 extra points of Leadership skill at 10% has a slightly better effect than another 10% bonus such as base proximity.
I don’t know why this is designed to work this way but bear this in mind, at a guess it allows you to rationalise employing better skilled Leaders more. Anyway going with higher skilled Air Leaders is a real benefit. Interesting I’d have to work it out but employ a Leader with 3 skill points more than one with the Night Flyer trait is better, although I’m not sure about one with 2 skill points above, but I think so.
Getting back to effectiveness between different Stack sizes and if bonuses including Leader skill points allow greater stack sizes, my experience tells me that there is not a difference between improving the ratio of efficiency, but while there is an increase in effectiveness in numbers and total strength points it isn’t efficient beyond a point really.
Most players would opt for 3, personally I opt for stacks of 4, netting between 63% to 70% of the value of that fourth extra squadron while for a fifth it ranges between 4-5% even after developing Mission efficiency several Levels and using high skilled Leaders and also increasing experience, very slowly.
3 is better than 2 or 1 effectively, even though at all times the efficiency difference is in favour of the smaller size because of the smaller Stacking Penalty applied. So IMHO it remains 3 or 4 or up to 5 (6 for INT/MRF) maximum Air Stack size no matter what the skill level of the Leader is, although as high as possible is best.
