My input is based on personal experience on a very solid wooden floor, not what people have said. I just got a GK 112, which has a 12" woofer mounted smack dab in the middle of a rectangular cabinet. Even with the tweeter turned off, my wife doesn't like the difference in brightness when it's standing on its end vs. laying down lengthwise on the floor. I agree that the lows are more accentuated when it's not on end, and I'm actually surprised at this difference because it has a slot port right at floor level when it's laying down.
But the best thing is you can test this easily. Have somebody sit some distance away in a chair facing away from you. Alternate between playing your bass with the speaker on the floor, and with the speaker raised. See if the person can easily distinguish the difference. To make it even more even, have the speaker angled slightly upwards when on the floor so that in both positions the cone is facing directly at the listener's head. Do this, and you can make up your own mind about what the dominant factor is between all the various contributing physics.