You say that the bullet must have exited at T1 , yet your graphic has it exiting at C7.
No, draw a horizontal line from the point the bullet hits JFK's back. That is the bottom of C7. The bullet actually exits at T1. But don't trust my graphic BTW, I was giving you the full benefit of the doubt to help you out. I just couldn't fudge it enough to make it work.
How have you determined that the exit wound was at C6?
What vertebrae is just below your Adam's apple? Better yet, do my laser experiment and SHOW me how the bullet entered at C7 and exited at C7.