I use binocs - both for 3d and hunting.
I shoot a 3d animal the same as I shoot a real one in that I pick a spot I want to hit.
With a real animal, the spot is based on hitting the center of the kill zone depending on angle.
On a 3d target, my spot is the center of the x ring. At the end of the round, I have a real record of how well I did hitting my aiming point.
In otherwords, every shot, 3d or animal, is a new shot that I am picking a spot on. In no way should shooting for x's on a 3d target make you ever shoot a real animal in the wrong place.
Besides, there is no way to have any marked kill zone on a 3d be reflective of real kill zones unless the targets are placed at an exact angle every time.
JMO
Steve