I think Ready was standing on the running board and was ducking after he heard the head shot. Very sensible, was Ready.
U can definitely see a fraction of an inch of Ready's dark shoes on the tarmac, doing what shoes do, ie taking steps.
In your overlay of QM u can see an inch of curb under the running board, on the far side of QM, even tho that pix was made from close.
Most of the youtube copies of Nix are lousy, but u can see the dark bit of shoe in good copies like the one in the frame that i showed.
But i admit that it aint very convincing/certain, even the good copies are blurry.
The running board stops near start of door, in my frame Ready is ahead of that point. But it is possible that he is hanging from the handle.
However, look at McIntyre, not worried about the sudden braking of QM at all, standing much higher than Ready & Landis.
However if Roberts is correct then Ready has not yet jumped down, koz Hill aint yet on the limo, ie if Ready jumps down after Nix has panned away from QM.
But i reckon that Roberts aint correct, & i reckon that Nix shows.
[edit][i now agree with Jerry Organ][see Reply#60.]