I'll try again then; didn't know it was possible. I've been unable to properly fire around any corners, but I am consistently shot by aliens through corner walls with 100% blockage. Or at least, there would be 100% blockage if I tried to fire along that same line.
I've seen other posting recently about the alien-shooting-thru-walls thing though, so that may just be a bug.
EDIT: Didn't see kabill's post. Alright then. So is leaning A. impossible or B. possible but it is just calculated automatically w/o an animation or TU consumption?