Say these offsets of POI that change when I reverse the mounts are 100% repeatable i.e. always 9cm and 4cm.
So I can just zero the scope for the centre of those two offsets. So with the mounts one way round the pellet is 2.5cm to the left and the other way they land 2.5cm to the right. Then I will know the scope is horizontally centred. Then I fix (shim or machine) the mounts to get it as central as I can, not perfect but certainly better than 1cm at 13m).
That would do me, just having it straight as possible horizontally, centring the scope vertically has less value to me.
Is life that simple?