Actually, the answer is quite simply.
It's a bell curve of tertiary, secondary, and primary skills, respectively, to their rate of parabolic growth. That means primaries are on top (HG gives you the most handgun bonus), secondaries follow (IRD), then tertiaries (Perception) and although it took rather a very long time to get enough data to actually figure it out, it was worth it; for a time. I had one calculated for the last skill system, if I find my old charts laying around anywhere I'll post them.. But
MA has changed alot since I last played, and unfortunately, all of those figures will be negated. It should give you a semblance of an idea though...
I had been keeping them essentially unbeknownst to the populace because of the obvious advantage it gave, but now that has no meaning... I'll look, if you care about the obsolete figures, and post them...