My son and I shoot quite a bit together.

We are both left-shoulder shooters.

When we shoot from sitting at 200 yards we obviosly shoot to different POI's. I cannot prove, but am certain this has do with the way the rifle recoils due to differences in hold. While the bullet is in the barrel, the gun is moving. The gun moves differently depending on what is bracing it. In this case, his arms and knees vs my arms and knees.

Looked at that way, I suppose it seems a wonder how any two people CAN shoot to the same POI.

You can play this game with yourself.

Shoot your favorite deer/elk/roo/buff/jaguar rifle from the bench. Use traditional bench technique {both hands on buttstock}. Now shoot with support hand pulling the forestock hard into the bags. Now shoot with support hand UNDER the front bag held hard. Now shoot with the support hand held under the front bag and the gun held loosely.

Your groups will probably be larger/smaller depending on method of hold, but look at the center of group. With many rifles you will see a group POI change.

No wonder it occurs then between two people.