Yes. Over time, one eventually witnesses all. Years back as we were preseason zeroing, we met a gentleman insisting we were doing it all wrong. One must zero firing from an off hand standing position.
There's actually a smidgen of truth to that. I noticed a lot when I was an avid smallbore silhouette shooter that I was off by a little with my offhand practice shooting versus benchrest sight-in. Differences between rest versus hand hold don'tcha know.
I've found the same thing. I zero from a rested position, but with the rifle held in both hands, and the back of my left hand on the rest, for the reason that that gives me a POI best representative of what I'll get for shots in the field. POI from resting directly on the bags front and rear tends to be different.
Wherever possible I take shots in the field from a similar hold: more often than not kneeling supported, or less often from lying supported or some other supported position, using some sort of improvised rest such as a post, stump, tree, or daypack. Offhand is a little different for POI, but I don't take the longer shots from that position - mostly quick snap shots, often at running animals - and so the difference isn't enough to matter.
