"the lower it is the more erratic the projections are and the higher the makeup the more precise they are"
Not really. That's a misleading description.
A better way to describe makeup is as a work ethic. A player can have a lot of potential physical skills, but if he doesn't put in the effort to achieve his potential when he's young, or put in the effort to maintain it when he's older, then skills will not develop as fully as they could, and will tend to decline more quickly.
Understanding, or course, that makeup is just one a a number of factors that go into progressing towards a player's projections.