RE: sighting in for different positions of shooting?
From doing exactly what you did, I can almost always see differences in confirmed zeros. I don't shoot anything less than 200 yards and at 200 yards the differences in zeros are small, on the order of a couple inches worst case scenario for me anyway.
IMHO the difference is often to the recoil differences of leaning into the gun vs "free recoil" of standing. I find that my zeros differ the most between standing and all the others.
Of course your offhand shooting groups will be worse, maybe much worse and it all can be caused by poor trigger control trying to grab what looks good vs accepting the wobble and squeezing through it.
End thoughts--- if you are looking through the center of your scope in all positions and at 100 yards I"d bet the total difference in zeros from all positions should be on the order of 2 inches or less.
Jeff