My AR is a very customized Noveske.   The COSUB on the Noveske was fired without shim, to determine a baseline for future zeroing.
1)  25 yards was a perfect zero
2)  50 yards was 3” high
3)  100 yards was close to about 8” high

Conclusion:  The COSUB should be zeroed to a particular distance, a distance where most shooting is likely to occur.  For my Noveske, I am shimming it to zero at 50 yards.  That means it will shoot a couple of inches low at 25, right on at 50, and perhaps 3” high at 100 — not bad when all other systems fail.  For a quick and reliable back up sight system (and even for a primary sight), at pretty much all practical distances, a 50 yard zero is the most prudent.  Next, we’ll try our COSUB, zeroed at 50 yards, at 200 and 300 yards.  We expect to hit a combat target out to 300 yards.  We’ll report on this soon.

Richard (ATS)