There is behavior realted to types. About genes specific for body traits of types there is no theory or experimental data.
As women breast contains fat, so higher body weight is _among factors_ which make them bigger.
While to higher body weight predisposes higher interest to material needs as meal.
S types women should have some bigger tits because of this factor, in average.
P.S. It's sad when a woman has low weight, as having it near top border of norma would give her the best look. Though, higher weight needs better developed muscles and so more of regular physical work. Everyday exercises for >= 30 min significantly help with muscles support (abdomen, legs, hands, etc). Having normaly developed muscles a woman with the said weight will not look "fatty" as a part of normal weight relates to muscles. She'll be more attractive and mb will have better health. With higher age arises the importance of positive factors for the health, and for the good look too. Do not overtrain - women are not men to impress by bending of steel pipes, some men can be scared by this.