hey
Vrelnir for the sizes how about have it be small goes in the hole no problem and large can't go in (note when you get smokes for Whitney and he/she has some fun with MC if stuck) with the in between sizes can go in but can't come back out.
also why not have it be the smaller the slower MC gains Physique (note have it slower with Physique being important and all)
and the smaller the more relaxed the NPC is at the start and with bigger add it so MC can get the NPC to stop raping the MC with the Demand action if the MC has a lot of fame in combat small has a tiny chance as well with the Bratty actions (note I feel like with Bratty actions on a smaller MC would just make them cuter the smaller the MC is) for the bigger size Bratty and Defiant actions being more of a turn off.
the run down bigger can get out of getting raped with words and are more of a turn off when being Bratty and Defiant.
and smaller having a slower Physique gain but can get in holes a lot more easy as well as being more cute when being Bratty and Defiant but Defiant only being cute if weak and or is with the Demand action.
(note can't tellsomeone is weak if they only talk big)
(note the reason I'm saying hole a lot is vore as in it should be more easy for things to eat smaller MCs)
hope some of these ideas help with fixing the sizes problem everyone is having.