I don't know how the couch is built but I guess it could absorb some sound depending on materials.
This wouldn't happen to be the listening couch because a subwoofer behind the listening position is probably the last place I'd place a sub.
I'd face the driver away from the cushion of the couch so that it's maybe firing into a wall where the pressure can disperse. If it's downfiring I don't think that a couch on one side of the sub will affect it too much.