We coined the term 'constant offset method' in the early 2000's to describe what we believe to be the proper way to accomplish zero with an IR laser ON A 25M ZERO RANGE (at the time, we were the lone voice in the wilderness). This was/ is important because, for mostly logistical reasons, most nighttime zeroing was/is done at 25m.
With this method, we account for vertical offset (height above or below bore) exactly as if we were zeroing our day sight. Our objective is to adjust the laser so that POA=POI at our zero distance (i.e. 200m). Doing so accounts for both height above/ below bore AND trajectory, each of which affect our zero in the vertical plane. When we have to shoot at close range (25m), we do ballistic calculations to determine the approximate up/ down shift in point of impact at that distance (i.e. 2.5 inches low at 25m).
We treat horizontal offset as an entirely separate issue. Because there's no significant change in bullet path on the horizontal plane, it's a simple problem with a simple answer- we accept the 0.75 right or left offset of the laser and maintain it at all distances. This gives us a known shift at close range and, more importantly, prevents the very dangerous converging/ diverging laser problem that a short-range POA=POI zero creates.
A final important note. This method produces functionally the same result as POI=POA at extended distance in the horizontal plane. Any time we establish zero on a short range, though, zero should be tested/ confirmed at our actual zero distance (200m) every time we are able.