Among other things, I'm a skeet shooter and have decided to purchase a semi auto shotgun. However, I'm extremely fussy about the sighting plane.

The gun MUST have a vented rib and further that rib's plane must sit slightly above the guns receiver. The front bead must not sit on the receiver when sighting the gun but must sit on the rib and somewhat above the receiver.

I usually refer to this as a "ramped rib" but am not sure that's what I should call it when asking others about the sighting plane.

Can anyone tell me what the proper terminology is for this type of sighting plane?

I always referred to that type of rib configuration as a "Stepped Rib" as apposed to a "Flat Rib"

Beretta 390s and 391s were made in both configuration.

As far as the front bead, I can't see how it would not sit on the same plane as the top of the rib. If it sat on the same sighting plane as the top of the receiver, it would be obscured by the difference in height of the step rib.

Even with a mid bead, the only way to see both beads is by looking down the rib, not the receiver Or if you are using a figure 8 to stack the beads, you'd be looking down on the top of the rib.

When I read the OP I was thinking what MG offered, I have both 390 and 391 that have that configuration if that helps your search. Sorry I can't help with the terminology. Good luck.