This year I started using a magnetic fiber optic sight on my waterfowl/pheasant gun (and similar on my upland bird gun). The sight I purchased rides on top of the vented rib barrel. If you look at the resulting line of sight (back of ribbed barrel and glowing bead) you'll see that if you `draw a bead' you'll be pointing/shooting low. I am gunning pretty much `instinctive' so any thought of thus `aiming high' vanishes. But I'm still getting birds. Now in a couple situations I have been able to actually observe the shot pattern at point of contant, and the pattern is indeed low (but, with modified choke, still grabs target with top of the pattern). I can imagine that with deliberate `bead' shooting and a full choke, one could miss under.
Note: the `extra' bead in the pic is a steel shot that leaked out of one of the critters on the way home and stuck via the magnets. We think. Anyway, I removed it before the next time out.