The whole zero thing is a mystery to me.
Whether it is from the bench or off hand zeros seem to drift for me. I have a pillar bedded Pharr 1712, and with different ammo, it still seems to change zero. I calibrated my home range with a Leica rangefinder, and I actually checked the paper target distance at Blue Rock and the separate range animals and they were all spot on. I was sure the distances would be wrong, but they were correct. I just sent back a new Leupold 25X, that seemed to have a parallax problem, that seemed to add to the drift, but I am sure drift will still be there with a new Sightron 6x24. I agree with other comments that a little elevation can be removed as the temperature climbs. This discussion also makes me think that I may try using a spotter.

You might have just missed an important post (Jerry G) which I have used personally to find out "holy #%^^*&" I am doing that!

If you practice shooting at paper you might find out you are moving the rifle.
It does not take much movement to throw off a shot.

Another thing is to practice your hold and pull the trigger but leave the rifle uncocked.
At times I was adding a slight movement when firing. It will show up there if you are pulling off taget while pulling against the spring.
It helped me anyway.

Jerry