I'vew often thought (just speculation on my part) that this issue may have to do with whether the (internal) receiver threads are square to the face of the receiver and/or the (external) threads on the barrel shank are square to the face of the shoulder of the shank. If a square condition exists with both parts, the shoulder of the barrel shank snugs up all the way around where it meets the face of the receiver, the barrel is going be pretty stable, and the more free-floated the better. If an out of square condition exists, it can create a "whipping" effect that can be stabilized by some fore end tip pressure. My guess is, this would not tend to resist thermally-induced point of impact change as much as having everything square to begin with. I think these same dynamics can exist as a result of a lack of concentricity between the OD of the barrel and the bore diameter. As I said, just speculating.
