PS2 player models are controlled by a few different variables:
Height, Weight, Face Shape, Body Size and Muscle Size are ones we've determined so far.
Here's a chart of a quick DOE I ran on what happens in the in-game appearance editor vs what I initially typed in vs what ends up being in the save file database once saved. The first columns are what my % I inputed. The 2nd column is what happens when you make that change, exit the appearance editor, and go back in. The game recalculates.... And the third column is what's in the save data afterward.
Trying to make a good body shape is going to be a challenge as the body size has really no correlation from what I can tell...
Except that when you start fooling around with the height/weight of a player, those numbers change magically on their own. The goal, then, would be to derived the formula used to come up with the percentages based on height and weight?