Fine.
Question: What's the first frame in which it's clear to you that he has leaned far to his right?
Will Z-150 do?
https://assassinationresearch.com/zfilm/z150.jpg
I don't think there is a frame from Z145 onward where that is clear. The limo moves from an almost head on view to being in the sprocket hole portion of the frame where the contrast is even worse.
What it comes down to is both you and I have tried to determine when the first shot was fired based on visible reactions. You find the turning of heads of various people to be an indication of a reaction to a gunshot and I find Zapruder's camera jiggle at Z155 to be the most compelling evidence. Neither is proof positive because other things could have caused people's heads to turn just as other things could have caused Zapruder's camera to jiggle. I find the camera jiggle to be more compelling because it closely resembles the jiggles following the second and third shots for which we know when those shots were fired. If you are comfortable believing the head turns are a more compelling indicator of when the first shot was fired, you are entitled to that opinion but don't act as if it is proof positive because it is not.