Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

No, Unger. The frame you put up from Nix was well after Z-255, so it has no relevance. Look at it this way: the cops were looking at JFK.

Hargis and Martin were behind and to the left of JFK, so they were looking forward and to their right. Chaney was in front and to the right of JFK, so he's looking back and to his left. 

If you use the Presidential limo as a frame of reference, Hargis and Martin are behind it, but Chaney is quite forward on it. He appears to be lined up with the middle of it whereas the other two are definitely behind it. So, Chaney is forward of Hargis and Martin.

And that's all that matters, what is going on in this photo and the Zapruder frame that corresponds to it, which is Z-255.

Again, Chaney's head movement tells the story: he was ahead of them.