I have an SBEII.
The small bead in the mid point on the rib is ever so slightly off center.
It's a little to the right of dead center.
I also have a new Benelli Ultra Light with the carbon fiber rib,
and I'll be darned if the mid bead on that isn't off center also.
The bead on the Ultra Light is not as far off as the SBEII,
but it is still off a little.
I don't use the center bead or pay much attention to the front bead when I'm shooting.
I just wondered why the mid bead is not centered.