The outer layer of the double is cut with a differential so the pad doesn't raise you up/so you don't feel the pad as much. It will depend on thickness of the pad to some degree. You shouldn't be able to feel the pad at all if it's up to around 2" thick, beyond that you probably would feel it some, but there should be a signifigant difference in "feel" between putting a thick pad in a single layer vs the sleeve of a double. With the pad in the sleeve, it shouldn't lift you up nearly as much as if you lay directly on the pad in a single.
I totally agree and that is the main reason I've begun favoring my air mattress over my UQ with the Ridgerunner, especially on long hikes where the chances of going to ground may increase.