It is also the case that he makes the fundamental error of Magic Bullet theorists that Connally is sat directly in front of JFK. We know that isn't the case. And, as you have pointed out, it depends on the orientation of the back at the moment of the shot and, also, the alignment of the limo with the SN.
Whether the SBT trajectory works depends on:
1. the time of the first shot. This determines the angle of the path from the SN to JFK's neck to the car direction.
2. the position of JBC relative to JFK. This includes the right-left and back-front position as well as
3. the orientation of JBC's back and left leg to the bullet path from the SN extended past JFK's throat exit point.
1. The angle of the path relative to the car direction is about 9.5 degrees at z223:

At z195 the angle is about 14 degrees:

The problem with most drawings depicting the SBT is that they don't get the angle right. This CNN drawing from 2013, for example, uses an angle of 7.5 degrees. This is 2 degrees less than the actual angle at z223 and represents the angle at around z300.

2. The CNN drawing also shows the relative positions incorrectly. While JBC was slightly inboard of JFK with JFK resting his right arm on the top of the car, JBC's jump seat was not that far inboard. Here is a photo taken on Houston just before turning onto Elm:

According to the H&E blueprint, the right edge of the jump seat was 2.5 inches from the inside of the door which was about .5 inches inboard of the inside panel next to JFK. So that puts JBC 3 inches inboard of JFK if JFK was sitting with his hips next to the right side of the car. That still puts JBC's right armpit well to the right of JFK's neck exit wound without taking into account the further right to left path of the bullet in traveling from JFK to JBC. Even if JBC was 6 inches inboard, it is still not nearly enough. His midline has to be left of JFK's midline by the distance from his midline to right armpit plus the additional right to left distance the bullet covered after leaving JFK's neck. That is about 12 inches. No one puts him anywhere near that far left (except Thomas Canning who put him over the drive shaft in his HSCA diagram).
3. There is no way that JBC's turn at z223-224 puts his right armpit to the left of JFK's midline. JFK has moved to the left and is no longer pressing against the right side of the car. JBC is no longer turned to his right as he was from z190-200.
So it seems pretty clear that the SBT trajectory has big problems. Much easier to imagine the bullet through JFK's neck going, as Dr. Shaw stated, to JBC's left side.
I completely agree with what you're saying here.
I don't want to get into a scenario where evidence is being planted but I'm in a bind - for me, the evidence that both men were shot through at the same time (z223) is beyond compelling.
I do not accept CE399 caused all the "bony damage" attributed to the various wounds.
I find there is evidence that the bullet fragmented on contact with Connally's wrist bone.
I'm left to conclude (for the moment, at least) that the Single Bullet theory is correct but that CE399 was not that bullet.
I agree with everything except your view that the SBT is correct.