Adjust your objective to the distance you are shooting at.
This will compensate for any minor "change" in your head / eye position while looking through your scope.
That is the benifit to having an adjustable objective !
If you shoot at 50 yards with your objective set at 200 yards, your point of impact will NOT be where you put the cross hairs (it's happened to me with a coyote that was a "chip shot" normally) !
The same is true if your objective is set at 50 yards and you are shooting at 200 yards. http://www.opticsplanet.com/riflesc...ry.html#01