content: I'm not entirely sure about that.  By putting the middle engine where they did it will cause the rear shockwave to be more gradual and hang back from the rear of the fuselage.  By stringing out the N wave that way, they might be able to get the sonic boom signature low enough that it can fly some over land routes.  I'm not sure if they're going for that, but I wondered if that might be one of their goals for building that test airplane.