Hi,
Michi Schweiger's (from NAISH) tip for the back foot position on a Naish board as starting point is back edge of the mast "hintere Abrisskante des Mastes". After that you should trim your foil as you like, more front or back foot.
Besten Dank Michi,
Gruesse an Robby,
Marcus aus Flensburg!!!
