Here is a photo of the hole in the rear of Gov. JBC's assassination-day suit. The hole was also enlarged to test fibers for metallic traces.

To be sure, if JBC's back was not at a 90-degree angle to the entering bullet, then you get a tendency to some elliptical or ovoid shaping of the bullet hole, even if the bullet is not tumbling. Different cloths react differently to bullets.
This angle-of-entry is also why JBC had a north-south ovoid wound in his back. The bullet struck JBC on a downward path. Moreover, if JBC was leaning back at the time he was struck, the angle of entry would be even steeper, enlarging the original would.
Still, most convincing is the small round entry round hole in JBC's assassination day shirt. How a tumbling bullet squirted through that small round hole in JBC's shirt is...well, a reasonable question.
My take is Gov. JBC was struck by a straight, unimpeded shot from the TSBD6 sniper window, or close thereto, and that is also the sentiment of his surgeon, Dr. Robert Shaw.
But hey, each to his own.
Caveat emptor, and draw your own conclusions.