This is my experience too. I've heard floorstanders with good imaging and excellent top and middle, but wooly in the bass which I put down to coupling with the floor. Very few floorstanders have a fast tight bass, it nearly always reverberates into the floor, I prefer distance between the floor and the speaker. Floorstanders need to be given a lot attention to reduce the amount of sound energy they put into the floor (particularly a suspended floor).
I spoke with the Kef guys a couple of years ago about the Muons being on the second floor at the Windsor show (they sounded amazing) and they said they spent a long time placing them and discovered they had to be over the the main beam in the floor to be good in the bass department.