Regarding sighting in with the rifle atop rests on a benchtop and held against the shoulder, I and others I've talked with often find zeros got this way are about 1 to 2 MOA to one side from zeros attained slung up in prone. They'll be to the left for a right handed shooter. Ones body mass position differences behind the rifle between the two is why.
Get zeros with both then compare their settings.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master