Real answer- proportions, your probably not giving your tit havers enough tummy, the torso should be 2-3 times longer than the base of the breast to look ok. A little can go a long way, making a "small" pair a lil saggy can make them feel much larger. If you want me to sketch out what I mean I can definitely do that for ya if ya need it.

Funny answer- *ADD MORE ASS TO COMPENSATE.*