With the coach above ride height the ride height valves have no effect on the air bags if air tight. The air bags do not have any " back" pressure from the weight of the coach if the chassis is suspended. This situation only occurs when the coach is above ride height and supported by the chassis. The lack of back pressure will change the amount of pressure required to actuate control valves and will also mask small air leaks. If there is a small leak in the suspension system, it will only be evident when the coach is removed from the chassis support. If the air system is used to lift the coach from stands this leak will not be evident as it is masked by the volume of air that is required to lift the coach from the stands. If jacks are used to lift the coach and not the air suspension the coach will not return to the same height as there is less volume in the complete system due to the small leak.
I speak from experience as I have had this happen. My old coach would hold air when suspended but would leak when on its own suspension. Basically, I had three small leaks but changing the pressure in part of the system changed how it would leak.