The saddle should be close to level. Casual saddles on casual bikes like the Nav can be tilted up in front just a bit to keep you from sliding forward. This is because the riding position is upright and the saddle is soft.

Your coincidence of crotch numbness and the urge to slide forward indicate to me that your saddle is too high. Leave the setback where it is and just lower it a bit until your butt is happy settling back in the pocket. Then call back and tell us if your crotch is still numb.