I guess this behaviour is because TD code consider basically aircraft weight and does not account particularities of the construction of each aircraft. I made some appointments about in another thread (LW vs REDS Topic). In principle i believe the g's must be quite the same because heavier a/c in general have more strong structures exactly to account this extra weight, and in part they are heavier due the strong structures that allow him to carry more loads and resist some g's.
I think it is difficult to account particularities of each aircraft since this depends of the existence of some reliable data about. This kind of info is not easy to find. All other way we ll simple guessing and prone to mistakes.
Envelope for P-51 Mustang:
P-51 FLYING ENVELOPE
