At Z380 - your choice - Jackie's hand is about 18" to 2' away from the continental kit on the rear bumper, sprawled in the middle of the trunk. Clint, obviously, is at the left rear bumper, behind and to his left of her. Her head, and Clint Hill's head are about 2' to 3' apart. Now Zapruder is also not, at this point, perpendicular to the limo. Your alleged optical illusion in Nix should then work, in reverse, with Jackie, in the foreground, overlapping Clint Hill, in the background. This effect is not visible in Z380, or any other frames.
No. Seen from behind and from the left (Nix view), they seem to overlap. Seen from behind and from the right (Zapruder view) we see the true separation.
Try looking at a couple of salt shakers, which represent the heads, a few inches apart and at a 45-degree angle between them. The one on the left, closer to you by about 3 inches. From the left and behind, they almost overlap. From the right and behind, they are widely separated.
By the way, I place it at z-375:
At z-375, Clint Hill is just the perfect distance from the standing man that is directly above him. Not z-374. Not z-376. It’s z-375.