In my experience, you center your scope vertically and horizontally. If your scope is set up properly, and things go as supposed to, you will loose between 3 and 5 moa to zero at 100 yards; that means you would have about 45 moa left of vertical adjustment. If you add a 20 moa base, you would then have 65 moa left for vertical adjustment.
My 300 RUM has a 20 moa base and I'm using them zee rings with 20 moa inserts for a total of 40 moa. My scope has 90 moa of total adjustment /2 =45 - 5 = 40 + 40 = 80 moa of usable vertical adjustment. If I get lost in spinning my turret, I go all the way down then back to zero and I'm in business!