Come on, man. Contributing is good but some of those chicks aren't small. Brianna Banks is like 5'10'' and DD.

Although size can't be based only on height, it does matter some. Generally I would consider 5'5'' to be the max end of small. A certain amount of "points" could be added or subtracted for skinnyness or diminutiveness of features such as breasts, butts, hands, face, etc. Weight is fairly important..

I think the most deciding factor is "does this chick make a cock look huge?" There is a reason why porn stars are not very tall. I would bet that a lot of them couldn't make it as models because of their lack of height and ended up in the porn business where petiteness is prefered. I don't think it is just some general preference among hetero-males of small women, it makes matching up male and female pornstars easier and all the more impressive.