Usually it depends on the scope, no?... My vortex scopes are kinda short on the eye relief so I used a scope rail that allowed me to move it back an extra 3/4 inch. It was positioned by how my cheek-weld is.

Also, I use a 2' long level sitting on a fence post across the yard & look thru the scope to level it. A string with a little weight hanging works ,too. Works like a charm....
Good luck with it.

By the way, I dig that camo.
Frank in Fla