Sounds like your rear mount is too low and you've run out of clicks.
Wind the turret completely down and then completely up to find out how many clicks you've got. Then wind it back to the mid point. At the range zero for height at 55 yards by only adjusting the rail (those without an adjustable rail use photo film in the rear mount). Then zero using the turrets for your selected distance (say 30 yards) ensuring your windage is spot on and then do all the other ranges.