but roughly on skill-sum.
I don't think that's exactly it. My player Wendon is pretty much at his cap (he is either there or a pop away from getting there) but has a skill sum of 103. That's a far cry from my approximate minimum - (somewhere around 50 for triple tremendous inside skills, a bit of shot blocking plus all atrocious guard skills).
I think it is more what Joseph Ka was saying. There are some skills that weight more against the cap, some that weight less. It is exponential like salaries, so that higher skills have more relative difference. But there is probably one cap formula for all players, not like salary where there are 5 different formulas.
Run of the Mill Canadian Manager