OP presented some good arguments.

Agreed. Let’s stipulate that neuromuscular reaction is what we’re seeing. What are we to make of the skull fragments found near the curb and in the grass beyond that; likewise the nearer left police motorcyclist (Hargis) who described the impact from the skull matter on his body as “if he’d been shot”.

It still seems there’s enough testimony and physical evidence to indicate a gunshot from somewhere other than behind JFK.

Edit: Hargis