Jenkins and Landis write in their 2004 book about the XB-70, regarding its inlet duct: "Three movable panels, positioned by two hydraulic actuators, opened or closed the throat area to meet engine air requirements; the maximum opening was 48 inches wide (doors set at 25.5 degrees) while the minimum was 19 inches (3.6 degrees)." The doors here are the bypass doors just before the engines, jettisoning the excess air from the duct. (There is a drawing showing four, not three panels, but this is not important fot the question.) So as far as I can understand this, when the panels opened fully (48 in), the doors too (25.5 deg). But this means the inlet sucking in lots of air but then the doors jettisoning the max amount they can. What is the reason behind it? Wouldn't be better a smaller duct from the beginning? Or I misunderstood the method here somehow?
Update: I tried to upload this pic before, but it was not working somehow. The bypass doors are somewhere near the right, about the "32.0" mark.