User blog comment:B214/Volume 22 spoilers/@comment-81.34.86.20-20161024091956/@comment-9595671-20161024142643

As I mentioned about, Diodora's queen wasn't the biggest in his peerage, and Sairaorg's Queen Kuisha may not be either. (I get the feeling Coriana may be considering Saiarorg sent her to battle Issei and strip for him)

It's not automatic for the Queen of each peerages' breasts to be bigger than every other girl in it. Ishibumi could easily play us and go the complete opposite direction because he all knows we expect that.

Though then again, if we go for unexpected... he might make Issei's Queen outsize Akeno, that would be a twist no one would see coming if only because there are characters like Gabriel implied to be bigger than Akeno, but he hasn't revealed another BWH stat for any female character for a while, even Grayfia doesn't have one.