Either the "guy" misunderstood what you were stating or he is an IDIOT. YOU NEVER LIFT THE REAR TIRES OFF THE GROUND, PERIOD. Regardless of ANY leveling/jack system. The only thing that HOLDS your RV in place,(especially on an incline) is the Parking Brake AND the Transmission Parking Pawl. So, with the rear tires off the ground, and your jacks with blocks supporting the rear of the RV, the RV itself can SLIDE very easily rearward and fall off the jacks. Has NOTHING to do with the length of the Jack piston. Doug