The ring around the sight is thicker on one side and thinner on the other (obviously).
The problem with that design is as you make an adjustment one way, say up, it would also move the point of impact left/right, whether you needed it to move that way or not. Plus, adjustment would be limited or "set" to whatever the sight gave you when you turned it. Hopefully as Gene says, there's some sort of other eccentric involved that would allow the desired adjustment.
