Originally Posted by Brian.Samson
This is a common mistake - It didn't occur to me actually until I found out by accident and then once I'd found out it seemed fairly obvious.
You only want your eye to be central to the scope IF your scope is optically centred and you haven't touched the turrets to zero it for windage.
If you've touched the turrets then the light and the image of the crosshairs will be slightly offset from the centre of the scope so you'd need to compensate by having your eye offset by the same amount from the centre of the scope line.
This is one of the main reasons to optically centre your scope and use adjustable mounts.
I have found this to be true , when using a Lightstream I had.
I used to make sure the outer part of the cross hairs intersect at the centre of the arc of the eyebell but to do this the centre was always offset to the left slightly .if that makes sense