The basic FR measurement dip has been shown. Im saying the audible Haas effect (theres lots of literature on this, Im not spoon feeding you) is hard to measure, and hard to correlate to hearing, not impossible. Yould have to measure the level delay and direction of all the reflections. Another problem with a hard ceiling, if your floor is also reflective, are flutter echoes, and these can be very detrimental.
You can try your own test with the floor. If its a reflective surface try throwing a thick rug where the sound reflects. If its a carpet throw some plywood/drywall on the floor.
If you can't hear a difference than you don't have to worry.