I put my mast at the same position for winging, sup foiling and down winding (with paddle).
I try to stand centered on the board with both feet and in a pretty narrow stance (hip to shoulder width).
The footpad on my board consist of 8 different pads with an inch space between them, so I can use that as a reference. A mate also gave the advice to put the board upside down (level), and use a string/rope to determine where the pressure point of the front wing is compared to the board and then mark that spot with a piece of tape or marker on the deck. Have not tried it. Think it's comparable to the "de Wild" method, but adds the marking your board on the deck.