The very first step, asks about floor level "a" or "b" B says that the Calibration frame and vehicle are not at the same height. It will allow you to put in the height difference and automatically calculate your height measurements.

   That's the calibration frame , then I think you would also be fine for the targets that mount on the wheel fixtures and calibration frame , but aren't  there other targets that lie flat at floor level  at certain distances to the sides that would still need  to be elevated to the rack level on something ? Maybe lay some  bricks or 2x4s under the fronts of a couple big ole wooden picnic Corn Hole bag toss platforms to bring em level about the height of the rack at ground level and lay the targets on top of them. Maybe a couple old Wack a Mole games placed along the sides and you wouldn't even need the targets. Ask what would Rube Goldberg do?  :-))