If you multiply the factors together (from the purple to get the blue) you get pretty close to right.
Which I did know how to do--but my spread-sheet fu screwed up and I was like "none of this makes any sense."
Let's take a look:
This is a picture of JAGS Attacks. At the top is STANDARD (ROF of S, roughly 2 attacks per round, and it does standard Impact damage--which is what all of these do for now).
Under that are the "atomic" modifiers (i.e. they are not combined with anything else). Rate of Fire 1, 1 round of charge-up between use (so it can't be used first round), explosive, and 8 REA Long action.
The numbers are "how much IMP damage this does with a 16 AP investment", "What the Percent Chance of Victory" was rated at by the simulator (note that ~56% is the 'right' POV. It would've been 50 but I changed the herds and didn't want to re-do a lot of work. So if the middle column is around 56% then it's "good." They all are, so they're all good. Factor is 21 (the damage the 'standard attack did') divided by the damage the listed attack did.
So if I had an ROF 1 power beam and got a magical item that added "+2 Ranged Impact Damage" I would take +2 / .72 = 2.78 (rounds to 3) so if I added the +2 bonus to the 1 ROF attack it would add +3 instead of +2.
So okay. Next, under the BLUE header are some combinations. You can see them all there.
I'll Post The Outcome Numbers Later
I re-did my calculations and it looks like it might work pretty close to multiply one factor by another ... Go Math!