Once you have your 100yds setting, you have to loosen the screws on the turret and turn the cap all the way down so the indicatior disappears and then retighten the screws at 0. Then you should have all the travel that is left in the scope with the indicator not showing at your real zero.
yes, about 3 clicks below my zero is where the stop is. Think I figured it out, when I was spinning the turret freely with the screws loose, I was hitting a false wall, pushed a little harder and the red pop up went down. Guess I just didn't force it quite enough. All good now.