I always thought the goal was to aim at the head with all kinds of weapons, but it's kind of awkward to aim at the head with a shotgun, so I didn't use them that much.Don't aim for the head with a shotgun. Aim for center of mass. In fact, I would only aim for the head with a sniper or dmr. Also I use the coyote sight for the shotgun because it takes up a minimal portion of the screen, aiming or not.
I'll try the coyote sight.