This is common to all of us.(Assume Right shoulder, Right handed)
The relative position of the LH controls how much the gun clears the body during mounting and how much the gun must come back to settle in the shoulder pocket.If the gun is 1" shorter than our norm moving the LH 1" further forward will make the mount feel the same. It will only be when the mount is complete and the gun fired that the LOP discrepency will show up as such things as thumb in nose, bruised fingers etc.

Hugh Lomas,
H.G.Lomas Gunmakers Inc.
920 876 3745