Is it beneficial to Hunker Down when I'm at full cover already?
Usually when I hunker down behind a bit of half-cover, the cover indicator goes 100% solid, as if I'd been behind a better bit of cover. It also gets a little outline and an "up" arrow above it.
However, the cover indicator is the same if I hunker down behind a piece of full cover. Is there any further benefit from hunkering down behind full cover? Or is it just a waste of a move?
Hunkering behind full cover works as advertised.
On the PC version of the game you can go back and left click on a unit after its move is complete, click the ? icon (or F1), and see his stats. I did a quick test on a support in full cover and his defense went from 40 to 80.
Also don't forget hunkering also gives immunity to critical hits... sometimes by itself that's not a waste of a move.