Well, although I have been down all three corridors, my greatest experience (including being used for formation practice by Soviet Mig 19s) was on the centre corridor starting at Hehlingen.
It was a 2-way corridor in the 1960s with 5 nms either side of centre giving a total of 20 nms width for the whole corridor. It is possible that my memory is letting me down but I shall look at some old charts next time I'm in the attic.