I would have made the max size 20 or something, but every level is close to 700 frames of animation I need to edit or at least duplicate and look over, so it would be too much work. The two extra cowgirl boob levels are exclusive to cowgirls because cowgirls have more powerful boobs than other characters, so the player simply isn't powerful enough. Also you can probably edit the savefile and set the boobs level of the player to 11 or 12, but the game will crash if you load the save and you're wearing a different bra than the cowgirl one.