There you go video demonstration. I know the guy personally and ridden with him, he can flatbase while not going on an edge. He taught me just imagine your body being an arrow and just stand still. Imagine if you just let a snowboard go down a slope (with nobody standing on it), it will not catch an edge. Now add a person on the snowboard and just get into an athletic stance bend your knees and ankle and don't make unnecessary movements with your upper or lower body.