KB--
IMHO, you are correct, that JBC's wound-shape and the small round bullet-hole in his shirt suggest he was largely facing forward when shot by a non-tumbling bullet from behind. That is what the evidence shows. That is what Dr. Robert Shaw, his surgeon, thought most likely.
We know what the Connallys testified to, and Nellie had a ringside seat, and was uninjured, and was remarkably cool in a same-day press conference.
So, if the Connallys are correct, when was JBC struck?
My best guess is sometime after Z-295, but before Z-313.
Of course, many, many witnesses described the "bang....bang-bang" cadence of shots.
That cadence lines up with JFK hit ~Z-221, JBC at ~Z-295+ and JFK at Z-313.
Caveat emptor, and draw your own conclusions.