I played around with the objects sinking, and I came to the conclusion that it had to do with the object's hot point. I don't know if there is anything you can do about it. I like the idea to use invisible floor above the visible floor. Moving the hot point or what about putting an invisible force field (ball) around the visible one, and have...no, the point would still be in the center. Moving it out to the end would work until it rotated.

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