I can't agree with the details of your theory but I agree totally that there were 2 different attacks under way. People who follow this case and have from Day 1 and who don't think LHO is responsible always had the problem that there is a awful lot of evidence that (to put it mildly) that LHO was up to something that day. OTOH, Lone Nutters had a problem dealing with the eye witness testimony that at least one shot did not come from the TSBD. Why not both?
Question: Where are the witnesses who said the shots sounded like they came from both the TSBD and this other location, e.g., fence, overpass?
If shots were fired from two locations then it seems to me that we should have had a number of witnesses - 10? 20? 100? - who said that: E.g., they heard 2-3 shots from the TSBD and another from behind the fence.
But I am not aware of a single earwitness who said that.
Correction: SS Agent Paul Landis said he heard shots both from behind - the TSBD - and then a last shot from front of the limo. He seems to be the only person in this tabulation that heard this:
https://www.jfk-assassination.net/earwitnesses.htmLandis said he first heard a shot that sounded like it came from behind him, over his right shoulder. Then this: "My immediate thought was that the President could not possibly be alive after being hit like he was. I still was not certain from which direction the second shot came, but my reaction at this time was that the shot came from somewhere towards the front, right-hand side of the road."
That's a pretty solid account but he is vague as to the locations.
So, as Enrico Fermi asked about extraterrestrial aliens: "Where are they?"