you.... what kind of heresy are you spouting!? tomboy usually have huge knockers somehow! the flat one is usually the frail petite girl! tomboy is usually quite large in body size (compared to petite girl), that's why they usually have average to large knockers to balance it out with the entire body.
when did you see a flat tomboy, again? as far as I remember, tomboy usually have medium to large knockers for the reason stated above. but my memory fail me almost on a regular basis.