Not familiar with this system, so apologies if im completely wide of the mark. but in certain naval games that i have played you roll for critical hits....sort of collateral damage that each hit goes beyond what the science would otherwise predict. you might get a Hood style hit in a magazine, or a Taiho rupture of the fuel tanks, that in turn leads to fatal damage to therest of the ship. Its dealt with generically by a critical hit roll...each hit generates a low probability of additional damage. I dont see why you couldnt have something similar in an air combat model. And that means that smaller rifle caliber hits whilst having far less explosive or destructive effect in themselves, might have a better chance of collateral damage because of multiple hits that they achieve.
The theory is pretty straight forward, but the research to get this right would be enormous, and might in the end simply be reduced to some sort of gusstimate. You might devise a system, punch in your estimated probabilities and then go off and test, and test, and test, against a known historical case or ten, and see if your estimated values produce the result that you are expecting.... if you do, well and good, if not, try revising your figures until you are getting roughly historical results from historical situations...