The beauty of the big boob toons is you can always tell which ones are dudes IRL. It's like the biggest dead giveaway there is.
Are you sure about that? I play toons of both sexes. MY female toons usually range around the lower slider limit.
To the OP: Have you tried playing around with the other upper body sliders to get proportions that make the breasts look smaller?
Personal pet peeve of mine have become the should width and upper body scale. Most players make them way to thin and fragile, even NPCs are "guilty" of that, which propels them firmly (forgive the pun) into anime land.