But at z195, JBC was turned so the plane of his back was aligned generally in the same direction as the right to left bullet path so the bullet would not necessarily have struck his back. We know it didn't. But that was not the only part of his body that was on the left side of the middle of his jumpseat. And there was a wound on his left side. What is "invalid" about that?
It would be valid if your 3D study was legitimate but it's a total conceit.
You see, the more things in a 3D analysis that actually relates to what is seen in the Zapruder film, the more confidence can be placed in it. I think I'm doing pretty good for someone on a consumer HP Pavilion trying to do something with SketchUp.
The Select Committee, Myers and NOVA (2013) studies weren't perfect (neither is mine, of course). But the best 3D studies just aren't finding that Connally was turned as much towards the car rail as you portray. Now it could be that you alone know more than these graphics experts or can see body positions on film that others cannot.
You won't admit to it, but to make your theory work, you were forced to move Kennedy away from the car rail more than he is ...
... and you stretched out the distance between the two men.