Going to have to check on Zo later for that (since I don't have sex scenes unlocked atm) because I feel that's wrong - B tends to make the cut off for their characters taking the hilt be anything less than 12... and logically you should be able to take anything in the butt deeper than a pussy so weird if they made anal the smaller requirement... but double checked Cait and that seems to only be the case for the Doggystyle anal scenes, if you let her cowgirl or you use wyvern venom I says your hilting her and I have an 11 inch dick. Not sure why Savin has that discrepancy with Cait between the scenes, probably an oversight.
Edit: Got to the point I can have sex with Zo again and I have a 11 inch knotted dick and in all her penetrative scenes she takes the knot so... not sure what you are talking about.