The MBUS sights are ones that I actually prefer them (at least the rear) to be mounted in reverse. If you look at the MBUS rear from the reversed angle, the pivoting piece that restricts the peep-hole to your "day-sight" is conical from that angle. From the intended rear POV, it's a flat surface with a aperture through it, which is fine it works perfectly. But if we remember our M1/M14 match sights and our M16 small aperture 'day-sight' it had a recessed or conical shape to it in order to recess the aperture to reduce glare and help us gain a better sight picture.
Try your MBUS rear sight mounted both ways, see if one may work better for you.
"If it wears out, replace it. If it breaks, upgrade." -Cranky Air Force Vet.
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