All my life, backing a tractor under a semi trailer, I watched to be sure the nose of the trailer came up as the 5th wheel went under. When Dad got his RV 5th wheel, he cut a beaded chain, put a weight on one end and a magnet on the other. To unhook, crank the legs until the bumper of truck just stopped going up. Pull out from under, hang chain so the weight was just above the ground. When ready to hook up crank until the weight is just on the ground. No way to high hitch.
To the class that are worried a pull test will harm the legs, chock the wheels! It takes some movement of the drum for the lever to force shoes to drum. But a wheel chocked tight will not let the trailer move.