This is a really good questionIf scopes can zero at 100 yards with a 20MOA rail then why ever not go with a 20MOA rail? Just curious.
I can't see .07" slope with a 12" long scope. And .035" higher eyepiece is probably not so noticeable when getting behind a rifle.As to why not, mounting the scope on a slope changes the look of the gun. That may or may not be a good thing. It also raises the ocular lens and requiring your eye to be further elevated above the stock. Again, may or may not be a good thing. As JE said, ideally the scope would stay optically centered. Depending on what issues may exist with a particular gun a sloped base may be needed to center the scope even at close range.