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It's a matter of leverage. Levers are simple machines and while not fully appreciated, they affect our lives all the time. A lever requires a pivot in order to be effective. Think of the pivot being the lower and upper cambands. The greater the lever arm from the work, the greater effect the same force will have. FWIW, single band BCs often allow the tank to pivot within the BC, so the bubble effect is not transferred efficiently. The bubble butt effect created by an AL tank is small, but it's there. The further back you put the bubble the better it can lift your butt. It's simple physics. We think in dry terms of balance. Sliding weight one way or the other will shift our balance and that holds true both in and out of the water. The counter intuitive part comes in when we neglect that parts of us have become floaty once we are submerged due to Archimedes' Principle. When it comes to tanks, steels operate just as we would expect them to while AL tanks work in reverse. Now combine Archimedes Principle with the principle of leverage and you can help get your butt back where it belongs by putting the tank as far back as possible... that is, if you're butt heavy to begin with.
