So it all seems to come down to the assumptions made by Myers and the Knott crew, about what were the actual body positions at the time of the back-to-neck shot (and if the bullet deviated in its path as it passed through JFK).
There is no possibility of the bullet changing direction materially after passing through JFK. It comes down to: 1. determining when the shot through JFK's neck may have occurred, according to the evidence, 2. what the actual position and direction of the car was at those times and what the body positions of the two men were at those times as determined from the evidence and 3. what the straight line trajectory of a shot from the SN through JFK's neck would have struck after leaving JFK, using an accurate 3D model of Dealey Plaza.
1. is going to be a range of zframes based on evidence. There are over
20 witnesses who reported seeing JFK react to the first shot and witnesses along Elm St. who said the first shot occurred just as the President's car passed by them or the President's car was "almost directly in front of me" or "after acknowledging our cheers, he faced forward again". Hugh Betzner said it was just after he took his z186 photo and was about to wind the film to take another. Phil Willis said that he took his z202 photo because the sound of the first shot caused him to reaction and press the shutter button on his camera. So that gives one possible range of frames to look at of maybe z190 to z202. The Connallys said that they thought that JBC looked like he was hit in the back at around z230 or so. So, assessing the uncertainty, you would look at a range from say 223-235. The WC said that JFK was hit around z210. Bugliosi thought the same. So you would look at a range from z205-215.
2. this is a matter of first of all having an accurate model of the car and of the two men. Then it is a matter of placing the car and them in the car and with the right posture so they appear to be the same as seen in the zfilm at the relevant frames. Again, there will be a range of uncertainty that would need to be quantified.
3. then it is just a matter of using an accurate 3D model of Dealey Plaza to see what a straight line path through JFK looked like for all ranges of times and positions.
The bottom line is that there is going to be a range of possible paths for the bullet through JFK at each of those times. Knott says that in any of those scenarios at z225 and z210 the trajectory through JFK does not go to JBC's right armpit or anywhere close. But they have not tried all the possible times. In particular, they have not tried a shot through JFK between z190 and z202 which is what I would be interested in seeing.