20 MOA should not bottom you out for 100 yards, it'll put you Near the bottom though and that's good since it gives you the Majority of your elevation adjustment to get out to 1000 yards. That's real important because a .308 rifle with 24" barrel firing Federal Gold Medal Match ammo with 168 grain MK HPBT bullets suffers a TON of bullet drop. If zeroed for 100 yards, that bullet is gonna drop 421 inches BELOW point of aim. You need over 41 MOA's to come up from a 100 yard zero to a 1000 yard zero...OUCH!
Keep in mind that the elevation adjustment limits in your scope's manual cover the entire travel from bottomed out to the bery top of the screw. So a scope with 80 minutes of elevation adjustment has only 40 minutes above and below dead bang middle. If your scope zeros for 100 yards at pretty much the middle of it's travel which most scopes do, you've lost half of your available elevation adjustment and a solid headwind, significant difference in elevation between you and the target, or less efficient ammunition, might eat up a lot of what's left. Frankly that sucks.
In my opinion, Scope mounts should be designed so that the average scope will zero in the lower quarter of it's elevation travel at 100 yards. Really you only need a couple minutes below 100 for in close precision work, but variations from gun to gun, even in a given model, make a 25% rule a good bet.
You will need AT LEAST medium height rings to get the front bell to clear the barrel by at least 4-5 mm. That depends upon barrel profile as well. The cant of the Badger Ordinance rail will affect this as well.
Call Premier Reticles and ask for their help.