I have often wondered if the back half of the P-38 is represented as a very large area that includes the empty space between the tail booms as part of the plane. It would explain the entire tail being shot off, which in real life was next to impossible.
Or it could just be the damage model. I think the damage model on the P-38 is either bizarreo ro buggy, or both. But I'm also pretty sure it has not been updated in AH II. I think Pyro said they'd do that and fix the 3D model at the same time, but not now.
If you look at a P-38, it has a very small profile from most angles, actually smaller than many single engine fighters.
I do know that no veteran P-38 pilot I know remembers seeing an entire tail come off of a P-38 except from a collision.
If you've ever seen a P-38 in person, it would be very obvious how hard it would be to hit both tail booms hard enough to cut the two stainless tail spars at the same time. Also, it wasn't easy to rip the tail off even if one boom was cut.