There are a few Kent courses that have superfast starts and manage to finish just short of the return hill. I think there are regulations concerning the distance between the start and finish lines so that a course designer can make a course "safer". Must be just lucky that as a biproduct the course ends up being a bit quicker.Do they still race on 'out and back' courses or are they different these days? Most of the ones I rode involved a turn at some point and a retrace, except for the F4, so if you had a following wind in one direction you got a headwind coming the other way.
Some of the times they are doing now are unbelievably fast.