Why Ashikagas land force limit at the beginning of the game is 19?
I see it's taking bonuses from each Daiymo but I have no idea why.
I wasn't able to find any LF limit bonus for Shogunate on Wiki page.
And it's before Sword Hunt decision has been activated.
Vassals grant the overlord 1+10% of their force limit as additional FL.
So every single Daimyo gives at least 1.3 FL to Ashikaga.
This can be increased by 'Vassal FL Contribution' modifiers, which Ashikaga has in it's NI's [One of three nations to have it; the others being
Bosnia and Andalusia]; and are also linked to Influence Ideas and certain policies and even Government Forms.
Notably the +Subject FL Contribution govforms are tied to being Buddhist; which Japan can flip to via event.
It's entirely possible to keep Ashikaga Ideas [Or never form Japan]; flip Buddhist and take Mandala System; and then take Influence and the required policies [Aristocratic and Economic] and get +500% Vassal FL contribution [Totaling +600%]
Which makes every Vassal give you 6+60% of their FL as your FL; and Marches give 12+120%.
Which actually makes it more efficient to build FL building in your subjects than your own land. Because the vassal gets +1/+2 FL;
and you get +0.6/+1.2 for a Vassal or +1.2/+2.4 for a March. With this setup building a +2 FL building in a March effectively gives you +4.2 total FL between the March's own army and your own.
You can also stay Shinto/Go Christian; and stay the Shogun and never form Japan, so you can have unlimited Daimyo. This cuts Vassal FL Contribution to +400%; but you can have as many vassals as you please. Provided they don't murder each other.