I have been asking for 40 years why a lone assassin in that particular room would have passed up the shot(s) you described and waited until his intended target was moving away at a declining angle to shoot. It makes absolutely NO sense unless he HAD to wait until the target was within the pre designated "kill zone".
BTW, I heard what was supposed to be the recording from the motorcycle cop's "open mike" and there were four bangs on that recording.
Also, have you ever seen the photo of the Lincoln's windshield with a bullet hole in the top window frame?
I have seen and read just about everything ever published, including the Warren Commission Report and the Zapruder film early on, about this event.
I was in high school when this occured. Three years later I was half way around the world learning all about "kill zones" and, at times, working closely with agents of a certian agency of the federal government.
I have also visited the site (Dealy Plaza) several times and have yet to come up with any answer to the question you posed other than what I have already said.