You believe the headshot came from the GK.
That's why you need the blowout at the back of the head.
But now that's been taken away, so we're onto frangible ammunition.
If a frangible bullet hit JFK in the temple from the front, his scalp/skull would've been blown to the back of his head and would've been hanging down
behind his ear.
But that is not what is shown in the Z-film. The large flap of scalp, with bone still attached, can be seen hanging down in front of his ear:
In the above pic, (for most honest people) JFK's ear is clearly visible next to the large piece of bone connected to the inside of the part of the scalp that has been blown down to the side. In his interview, Jenkins describes the large head wound as scalp and skull opening away from the side of JFK's head. The impression he gives is of a large, hinged flap of scalp that could hang down by the right side of the head. This large flap of scalp is visible in the Z-film hanging down by the side of JFK's head.
In the clip below pay particular attention to the large, pendulous strip of scalp that seems to sway forwards as JFK begins to collapse forwards:
This large portion of scalp is picked out by the yellow arrow in the frame below:
It makes sense that this portion of scalp would have been blown down behind the ear if a frangible bullet, fired from the GK, hit JFK in the temple area.
The wound to JFK's head is most probably a tangential gunshot wound. Pat Speer deals with this in immense detail at his website [chapters 16b and 16c] patspeer.com