I'm not saying that you can't go faster by getting your butt low. I don't like to do it because I find I can toss the bike back and forth faster if I'm on top enough to put weight on the outside peg, like a skier. Racers obviously don't do this because their feet aren't even on the peg sometimes. Maybe my body can't move my butt fast enough to get the bike upright again even with less lean angle to start with. And maybe groups would drop me because I'm riding too slow because I have the bike leaned over too far and need more time for road hazards.
I'm confused by the talk of changes in the size of the contact patch. I see this discussed in a lot of places, but I'm not sure it's all correct. The contact patch is determined by the pressure in the tires, the weight on the tires, and compliant or stiff tire construction. If the side walls are sufficiently compliant, the tire patch changes from shifting weight fore and aft and by aerodynamic forces. Also, in a turn with sufficient banking you should be able to weigh the bike down with speed. I could see how shifting body weight side to side could change the shape of the contact patch, and thus affect direction, but not so much the size of patch.
Which brings me back to tire lean. Maybe this example is oversimplified but we've all been shown the styrofoam cup turning because of its shape. When you get a bike tire on its side it can change direction. If the bike geometry allows it, and you're going fast enough to not fall over, you don't even have to turn the front tire in the direction of the turn. This is easy to demonstrate with a roadie style bicycle. You can grab the bike by the stem and change direction just by leaning the bike over.