I think you're very confused, Chris. First, your drawing remarkably almost matches mine. I'm assuming, though, that your red X is Altgens? If so, you're wrong about that, Chris. He was up much further than that. He's out of the frame in Muchmore because he was up further on Elm.
Second, Altgens marked himself on CE 354 exactly where he was and can be seen in the Z film. Any serious researcher of this case sees Altgens as he's standing in the exact same position he points himself out (#3) in CE354 as you see him in the Z film. This further negates where you *think* he was in your diagram.
Third, he said he heard no more shots after the head shot. This is accurate and is also accurate from other witnesses. The shots stopped after Z313.
Fourth, Altgens said he was "about 15 feet away" from the head shot, which is more or less about right. If you look at CE354 where he marked himself and then allow the car to move a little bit further down to when Z313 takes place, it's exactly in the same position as the diorama, the Muchmore film, the Z film, and the Nix film. Please don't hold it against Altens though, Chris, if his "15 feet away" quote would ever be inaccurate. It's just an estimate from someone who was where he said he was but didn't go back seconds after it was all over with a measuring tape to get the exact distance.
Fifth, as your blue X marks as well as mine shows, that blue X is roughly where Altgens said he pointed his camera toward and took his final photo showing Jackie up on top of the trunk (or climbing back in rather) with Hill up there too. With no witness at all reporting, including Altgens himself, that no other shots were ever fired this far down the street and all shots ending at Z313, it's impossible for more shots to have occurred like you think they did way down by the blue X.
Sixth, people make mistakes, Chris. All kinds of crazy reports were coming in minutes after the shooting took place. Witnesses have said some pretty goofy stuff in this case. Altgens was obviously where he said he was, but we shouldn't hold him down to being exactly and precisely "...15 feet away." And yes, there was a conspiracy in this case, but just because the FBI agents made a mistake in putting cars on a diorama too far down the street, then realizing their mistake and moving them up to the actual and correct position, doesn't mean something sinister took place.
Seventh, the FBI got it right the second time around with their diorama, Chris. The first time was a simple mistake that they corrected and was not corrected because of some nefarious reason, Chris. The proof is all of the films mentioned above match up perfectly where the final shots at Z313 take place. The old guy - looking upward and facing the Muchmore camera - reacts perfectly to these final shots that took place.