I'm sure it was Boeing who did some research
I'd be interested to read such research... at that time seat standards were a bit average and I'd be more concerned about the seats tearing free from the mountings under realistic crash loads.
as by airborne objects (baggage, detached cabin fittings, etc, even unbelted pax from behind)
if such occurs, then the crash loading is reasonably high .. see previous comment ..
A Brace Position will take your head completely out of the prime trajectory of such items
I suggest that the more worrying crashes don't involve sufficient warning to do anything .. far less "brace for impact" ..
whereas rearward-facing seats offer no such protection
.. granted .. but they do offer an improved probability of non-disablement and residual ability to exit the aircraft under one's own steam ..