Just installed a new Bushnell E62440 scope on a DPMS LR.308 flat top. At 100 yards, the point of impact was about 8" low. So I adjusted the elevation to correct. But then I thought, how much more adjustment is left for longer shots...not much. So I shimmed the rear bout .035" betweent he rail and the bottom of the rear ring. That put me about right where I need to be with the crosshairs neutral (in the middle of the adjustment range). But why should I need to shim that much? Is that normal? What could cause this much miss alignment? Is that going to cause a problem?