Not atabea, but I can address that...
I originally had my Crowsons directly on my floor, (carpet over concrete.) At the same time, I also had a friend with a powerful subwoofer system on a suspended floor. Both systems provided similar tactile response. The key difference I noted between the tactile response of his system and the tactile response of my system was that I could sense the floor motion in my feet in his system, but not in mine. It felt odd getting tactile response through my entire body, but not feeling anything through my feet on the floor.
My seats reclince, so my initial "solution" was to just recline the seats so my feet weren't on the floor. Then it felt very natural.
Eventually, the more permanent and complete solution was to build a suspended riser for my seating. The Crowson's shake the seating AND the riser, so I get tactile response through my body and my feet.
Just to be clear, no
tactile transducer/shaker that is attached only to the seats will provide tactile response to the feet unless the seating is reclined. For *any* tactile transducer to shake the body as well as the floor/feet, it needs to be attached to a shakeable floor, (i.e., a riser), as well as the seats.
I wouldn't let the "concern" about tactile response not being sensed through the feet be a deterrent to the use of the Crowson's, or any other shaker/tactile actuator. The sensation they add is beneficial, even if the feet aren't included.