One of the toughest things to learn in any mechanical type connection is when is it tight and when is it too tight(or loose). Good mechanics, pipe fitters, electricians etc. learn that just right feeling over time. I don't use alot of romex connectors but I can't ever remember worrying about bottoming out the screws to make sure a cable wasn't going to fall out or be loose. Seems to me you're being alittle too aggressive with the screwdriver
