Basically what's being said is that different skills have different salary jumps in each position.
There's not much of a salary balancing more so than getting the best bang for your buck.
An example would be a center with 9od vs a center with 2 od. The performance would be quite a lot better in the first case but the increase in salary would probably amount to 1k total. (Just a guesstimate)
In general offensive pops cost more salary than defence.