i think surgeons have an idea of where the soft tissue will sit after doing hundreds and hundreds of surgeries. but they dont want to make any promises in the event their prediction doesnt churn out they way they think it would.
i dont think race matters much. soft tissue is a direct reflection of the hard tissue. your soft tissue is completely genetic - it's density, thickness, all of that is defined by genetics and it doesnt matter how you grow it will always be the same.
BUT, your hard tissue is malleable, and if the hard tissue is distorted the soft tissue is going to be warped and look off because it is NOT malleable growth-wise. it will stretch, bend, or sag according to how the bones harden on your face.
this is why a lot of people with say, long face syndrome tend to have a very similar facial type. the soft tissue unnaturally lengthens, or "stretches." one of the biggest drawbacks is the loss of support. gravity will does a number on your skin if your bones arent projected forward enough.