No it's much more complex. Too complex to just explain here to you. Go to buzzer-manager.com and play with the salary estimation tool, that's the best way to learn.
There are no simple numbers that you can use, there are too many variables. If you have a Center with 100 TSP, 20 each in REB, SB, ID and IS and a little in the other skills, he'll need ATG potentiall. However if you distribute the same 100 skillpoints as 10 over all skills you can stay within All-star/P. Allstar range. Secondary skills count less towards potential cap.
You can't say there's a salary point where a player caps, because two players with the same salary can have completely different skills and potential. Just play around with that salary tool and find out.