[WhoDatNotSayin]

I think it has been more or less definitely shown that stock IL-2 doesn't model changes in CoG with fuel load.

I'm not sure this discussion of FMs is getting us very far though. From what I've seen there are only two sensible approaches to this: (a) apply general aerodynamic principles to data available for the aircraft under discussion, or (b) refer to actual flight-test data.