I don't quite understand the question.
Potential cap is based on skills, not salaries. But salaries are based on skills. So potential cap is loosely based on salary.
So in the post above I indicated the approximate salary at which a player with that potential will hit the soft cap.
You can still train after you hit the soft cap, but training is much much much slower! And is not worth doing.
So a player the 6th man potential could cap at 10k or could cap at 15k (just examples) because of different skills and hence different salary. So the salary is just an approximation, but you will know when you hit the soft cap because training will take forever lol!