@Hwy1North: Thanks for your comments about your stance and its variations in different disciplines. Your points are well taken: 1. about bringing feet closer and more central, and 2. turning vs. long-distance pumping (or simply pumping to stay on foil in a lull).
Most of my practice is with my wing de-powered, so I can usually cheat and save myself, and this has made learning more forgiving but slower.
I've realized that, for steering when pumping, both of my feet (mostly rear foot) can traverse somewhat laterally, although not as much as when winging. As long as I maintain some overlap with the centerline with either my toes or heal depending on the foot and turning direction, I am still able to pump directly over the centerline by pushing from that part of my foot.