I'm sure a lot has to do with pax/bag loads ... if there are only, say, 40 checked bags, it's fairly easy to see that none have reappeared 'behind the wall' once the last one is off the cart ... also, the belts at DCA make a 90-degree turn and parallel the wall for ~10 feet before and after the longer section that's perpendicular to the wall
found this in
google images search for "baggage claim DCA"