Isn't "
the moment and position of entry" saying that you should assume both vehicles' respective CAs are the same as they were immediately
before the moving AFV crossed into the other's hex?
That's the only thing that makes sense to me. But, wow, what a badly written rule! What about that last sentence:
A vehicle thus barred from remaining in an AFV's hex may not attempt ESB in that hex.
If the vehicle didn't MPs remaining and can't attempt ESB, what effect is "barred from remaining..."? I guess D2.6 is simply prohibiting the vehicle from entering if it couldn't leave, but it seems like it could be stated much more clearly.