If a person is shooting LOW with a shimmable gun like the Benelli, to me the correct fix would be to reduce the drop of the stock. That is exactly why they give you shims. I doubt Benelli would want you to use taller beads or they would supply a few different beads.
The old acronym for adjusting sights holds true: FORS, can help you remember that, when it comes to changing where your shot strikes, the Front sight should be moved in the Opposite direction and the Rear sight should be moved in the Same direction as your intended point of impact.
If you are shooting low and want to raise the POI of your shotgun, you just need to raise the
rear sight, the EYE. So you shim for less drop, IE: a straighter stock.
Further, most every shooting coach out there will tell you that the bead or beads are only there to check your gun mount/alignment. Once properly mounted, the coaches tell you to focus on the target, not the bead or barrel. This is where practicing a good mount comes into play.
If one is shooting BEHIND the target, that's a problem with lead. Proper gun mount, focusing on the target and not stopping the swing is generally how you get proper lead. Well, that and a lot of practice too!
