Yes, specifically it did go backward and to the left. That's indisputable. And, yes, the 6th floor SDB window was back and to the right. However, Kennedy's head went backward and to the left, which leads to...
" For every action there is an equal and oppopsite reaction."
The grassy knoll was forward and to the right, the opposite of the direction of JFK's head's motion. After having personally walked all around behind the fence that's behind the grassy knoll, I feel the final shot came from behind the fence at the corner up by the railroad tracks.
And, my first visit behind the grassy knoll was in the early 70's when it was still a gravel and dirt rail yard and before the new parking lot and other changes to the general area associated with the West End.
The grassy knoll was forward and to the right, the opposite of the direction of JFK's head's motion.
If you agree that every action has an equal and opposite reaction, then his head moving backward and to the left may be inconsistent with a shot being fired from the front right.
My view is that the wound on the back of Kennedy's head was an entrance wound, and that the much larger wound on the front right side was an exit wound. I believe that the force of his brain and blood exploding out of front right side caused his head to move backward and to the left. The exit wound would have had a much more profound effect on the ultimate motion of Kennedy's head than the entrance wound would have, because the exit wound was so much larger.