I tried to make the retinue buildings increase retinues by a percentage, but it wasn't working very well as the starting retinue cap is really really low, so even if a building increased it by 100% it increased it very marginally compared to just using flat numbers. Right now if you have the max 16 demesne holdings and maxed retinue buildings in all your demesne, you should have a retinue cap of 64000, retinues have higher morale and organization that levies, AND you should still be getting a substantial amount of vassal levies unless you have max Tax laws (with just Myr, Tyrosh, and Lys, I'm able to get 25-30k.)
well i didn't mean that it should only be percentage, the idea of the camps is good, but they give too much too soon (in my opinion), if instead each camp gave 2000 fully upgraded, and you added somewhere a percentage modifier based on realm size lets say +0% up to 150/ +50% up to 200 / +500% on realm size 500 or some numbers like that, it would provide the ilussion that you are getting recruits from the provinces to train them in your camps,
Another thing, the camp modifiers hile they do make some sense they arent exactly what i feel they should be. Unless i am mistaken which i could be, troop modifiers only affect retinues when on your capital, so they are mostly fluff in your camps (you dont get any levies that profit from it),
the tax modifier... well you have your reasons, i just don't understand/share them, #For Balance / More hands to plow the fields, etc. etc. for those reasons i think it should be instead a modifier to garrison, because building those camps make it so siegeing your counties becomes a walk in the park, when at least in my opinion, if i have a huge ass training camp near/ inside some of my cities/castles it should make them MUCH MUCH harder to siege rather than easier (you can send the trainees to man the walls).
TLDR: camps should give a flat amount of retinues (just a tad lower on the higher levels) and increase the garrisons of the province, in your capital holding you shold get the bonuses to the troops (so the retinues get it) and a percentage increase of the reinue size as your empire grows as a character modifier akin the reduced retinue cost you already get.
it is my opinion that it would make it feel more like a growing empire when you do expand, and would penalize less those that prefer having a few cities in their capital so they can swim in gold. (it would still be a trade-off)