In re-reading your original post I assumed you wanted to ensure that the sub did not move around and did not cause bass loading to your flooring. Once I re-read it I came away with the idea that you have an issue with the way the driver is loading the ports inside the sub. If you are having what some refer to as "port chuffing" due to air movement through the port, increasing the distance from the floor may affect your ability to hear it somewhat. The GRAMMAll is designed to both elevate and isolate from the floor. It is carpeted to ensure the chuffing is somewhat absorbed also.

Even if your house sits on a slab the sub has the capability to transmit significant energy to the floor and around the house at high volumes and low frequencies. If you want to do an experiment, play a 20-25 hz test signal through your sub and walk around your house to listen for items vibrating. I do this anytime I set up a new room to make sure everything is going to stay where I put it.