As with many - my rear window has separated at the bottom - inside and out. I purchased epoxy - the inside looks pretty easy. The outside flap at the bottom is coming up maybe 1/4" short of being fully seated on the window. I suspect it has been loose for a while and shrunk a little. Does anyone know if I can loosen the steel clamp inside the car (under the window) in the back to gain a teeny bit more material? Or am I asking for trouble by releasing that tension?

You already doing this? Release the two front latches and hit the retract button for about a half sec. That should release any tension on the top.

Yea, that will work - but my concern is after the epoxy sets up and now I close the top - if there is not enough canvas as it appears, the repair will just pull right off when stretched to the limit.