Mobile lounge - I hadn't heard that term before! I can think of some less flattering names! The only additional tip to add to the above is that if you want to be near the front you're better standing in the little alcove in the middle rather than off to the side, as that spot might be needed for a wheelchair and if it is the driver will have no hesitation on marching you to the back.

But to be honest IAD is a lot less of an ordeal since they installed the kiosks. If you're on a returning ESTA then you'll be through in 10-15 minutes even if you don't fine-tune your journey from the plane to the immigration hall.