EOP?
Cowlick?
And the answer is...both!
It's pretty simple.
Your line about JFK needing to be " slumped forward" - I paraphrase - explains it all.
Why the need to assume a “slumped forward” position? Either the EOP or the Cowlick can be hit from the TSBD sniper’s nest.
The need for a “slumped forward” position is only needed if one does not understand that bullet fragments do not always follow a straight path through the body. Indeed, in general, bullet fragments follow a curved path. This is something any true ballistic expert can tell you. And has clearly demonstrated many times with photographs of ballistic gel blocks, after they have been shot with an embedded bone target, resulting in clearly visible curved paths in the ballistic blocks formed by the resulting fragments.
But this was something that was not understood by the HSCA. Hence, their totally unnecessary “slumped forward” hypothesis. To allow a straight line from the TSBD sniper’s nest, through the cowlick entry wound that they “deduced”, which allowed a straight-line path through the exit wound.
Of course, this explanation is no good. It goes against what is seen in the Zapruder film. And because of where the fragments struck windshield frame and windshield, which are not anywhere near this straight line. And is totally unnecessary because a bullet could strike either the EOP or cowlick, follow a curved path, exit the exit wound and head straight for the windshield frame or windshield on slightly diverting paths. It is just more plausible if the bullet struck the EOP. The resulting curve is less extreme and simpler than the curve that would correspond to the cowlick entry.
But, CTers will happily continue to site this gaff by the HSCA even though this “slumped forward” hypothesis has never been a leading contender among LNers. But CTers will continue to pretend that it has been and still is.