The ground floors in our Home are solid concrete, which I think were screeded and tiled and then we have underlay/carpet. I find therefore a Sub works well on the floor and my own preference has been to put a sub in the corner of the room out in front of my listening position. I don’t like the Sub behind me nor under the couch like many may opt for.
I’m lucky with my lounge, as I have an extension on that room which gives me a corner in the centre of the room between the stereo speakers and that is the position where I have chosen to put the Sub. I’ve not ever considered raising it up off the floor, but I don’t get vibration. I’m also not one that likes the Sub output so high that it rattles the windows, or glasses in a cabinet - I prefer the Bass to be more subtle.
Usually the default setting is enough for my ears, my Wife prefers less, my children (who have now flown the nest anyway) would likely prefer more Bass.
But all that aside, the answer of where to put any Sub is …where it sounds best to your ears.