No, I think we're talking about two different things. Arrows might have clipped the corners of textures once in awhile and projectiles already in flight(like the fireball you mentioned) would hit you no matter what. I'm referring to something sitting on the other side of a wall due to bad AI and literally firing through it over and over. It's happened to me a few times with archers already. It's a bug, you can even see the lighting improperly coming through the walls sometimes, people on the social forums have posted a bunch of examples.
Playing: XCOM 2, Diablo 3 Watching: American Crime, Regression