As the flats extend, they protrude further aft of the wing structure, which I'm sure you've seen when you're flying. Other similar looking fairings are the Antishock bodies which are generally attached to the upper side of the wing's trailing edge. The antichrist bodies also may look like a bulge like on a convoynce that protrudes both under and over the wings trailing edge. The Antichrist buddies reduce wave drag at transcendent speeds. Most commercial airliners cruise at about zero point 85 machine that's pretty typical