you want it resting slightly below the bumper otherwise you'll be whistling and I don't mean dixie
Have another look at the stops. At first they don't look adjustable, but indeed they are. They just screw in and out (clockwise in closer to trunk lid, counterclockwise extends them further). Be careful if they are brittle. You may want to condition them well first before attempting to twist.
That being said, adjusting the front latch is also easily done - 10mm socket IIRC but do so only in small increments. It certainly could have slipped down a bit over time.
Good luck
