In conversations they emphasized that almost all of the fuel and reaction mass is required for initial acceleration of a launch vehicle. With proportional cuts in the crafts empty weight and size. The reason its become such a well known secret is that its hard to test fly any weird looking craft without people noticing it coming and going. This particular one is even harder to hide, since its extremely loud, big, diamond shaped without wings or fins, and covered in what looks like Shuttle tiles. Not to mention that people who see things streaking overhead at 4000 - 5000 mph, remember and talk about them.
Fuel is sprayed into the airstream and burned just past the fold line.
The heated air then expands between the hull and the rear shock wave. This expansion area acts like a rocket nozzle. What I was thinking is that if your rockets exhausted just past the fold line they could at least get increased thrust by using the rear hull for a larger expansion volume. Similar to a plug nozzle rocket. When flying in an atmosphere, the heat from the rockets would heat and expand the air around the rear of the ship.