I think it's pretty much accepted that soft tissue adaptation to maxillofacial surgery is a crap shoot. The planning software helps, but cannot be relied upon. I'm wondering if having a low body fat % will help:
a) make it easier for the surgeon to plan the surgery
b) make it easier to perform the surgery
c) allow the skin to "shrink-wrap" around the the bones better
d) all of the above.
I went from about 77 kg to 69 kg in the last 4 months. My (albeit meagre) cheekbones have revealed themselves for the first time ever. My chin doesn't look as pointy as before because the face is narrower (and I'm now considering the surgeon's advice that maybe I should leave it well alone). OTOH, my retruded maxilla is there in all it's glory. In profile: concave face, absolutely huge nose. (But at least I have something resembling an S-curve!). It also took some time for the skin to follow the fat loss. It looked almost saggy at first. But then I'm 36 (although always told that I look younger, no wrinkles).
But then I often hear that one should go into surgery with a few extra pounds. I asked my surgeon about this and he emphatically said "No".