Vertical adjustment off axis - Vortex Viper HS 4-16x50mm Rifle Scope, 30mm Tube, Second Focal Plane

Optics Planet provides great service and for the most part carries excellent products. I have purchased a number of rifle scopes from Optics Planet. Recently I purchased a Vortex 4-16x50. After mounting the scope and being certain that the crosshairs were true, I found that I was having difficulty sighting in the scope. With minor adjustments in the vertical the point of impact would move the the right with downward adjustment and left with upward adjustment. This was checked against a plumb line at 100 yards. Unfortunately the scope is beyond the return date for Optics Planet, and I will need to return it to Vortex for repair or replacement. I doubt I would purchase another Vortex scope.