It does make sense that, after the long run-up for the dirt mile (172 feet), the run-ups for the longer two-turn dirt races taper off steadily after that.
By the way, the run-up at 1 1/16 miles on the "all-weather" at Arlington - no more auxiliary finish line; see
this link - is 150 feet, and the run-up for those ridiculous 1-mile dirt races at Keeneland is 210 feet, in addition to using an auxiliary finish line - and they had the nerve to run a Breeders' Cup race (the Dirt Mile) under such circumstances?