OK, so when I installed my Holosight on my R22, I ran out of elevation adjustment with the POI still 1 inch below the dot.
I dismounted the shroud and installed a .040 washer under the rear bolt. It snugs down with barely any visible gap. If my math is right, it should give me up to 17 inches of elevation, which should put me back in the ballpark. the gap around the barrel at the opening of the shroud looks fine.