RE: Beretta customer service sucks
Have you talked to Rich Cole at Cole Gunsmithing? I'd talk to him and see what he thinks. Honestly, it sounds like a gunfitting issue. How did you fnd out your gun was shooting 10-12 inches low, were you on a bench rest sighting down the barrel or were you mounting and shooting offhand? I know you're not a novice but most shotguns will appear slightly uphill depending on the POI preferences of the shooter. If the gun has two beads they will form an 8 with the middle bead being on the bottom. Of course I can't tell how much rib you are seeing, but you should be seeing some of the top of the rib.
Gordon