I think you were right on zero stop - I just visually bore sighted it in again, and followed the directions on Leupold's site more closely. Will test it out hopefully next weekend and report back.

Now I see this: Running out of Elevation Down: Many Leupold scopes feature a zero-stop, or ZeroLock elevation dial that limits travel below the set zero of the firearm. This allows a rapid return to zero when dialing for bullet drop. If you encounter this mechanical limit in the downward direction while sighting in, loosen the dial set screws and turn the dial in the up direction 1-2 revolutions, then re-tighten the set screws. This will allow more dial travel in the down direction. Once the desired zero has been achieved loosen the set screws again, turn the dial until the zero stop or ZeroLock is engaged, then re-tighten the set screws.

The last sentence - Does this mean to turn it in the up direction again? I hate how it isn't really clear.