Normally an approach speed is 1.3 times the calculated stall speed which allows for the landing flare. A shallow approach needs less energy/buffer above the stall speed to flare. Without a 50' obstacle one can land earlier, carry less approach speed and the landing run will (a) start earlier and...
I visited the camp in May 2006 put up a video of Harry here:-
Stalag Luft 3 - (good quality video) - Google Video
Last year I hired an aircraft and took some aerial shots of the camp.
Email me rsvp99(AT)gmail.com if you'd like any 'photos.
Thanks.