There's no rib visible, basically just the apex of the front sight triangle visible over the ramp. My other M2 has an XS rear sight, and I can see way more of the front sight and still have POA/POI.
It has a nordic clamp, but I didn't think it could have THAT much of an effect. I'll take it off and see if that helps.
They're Fiocchi JM slugs, which shoot great in my other M2. They're grouping great (maybe 5" at 100yds), just way high.
Andy