I'm no expert but I'm thinking your rear foot placement in relation with the mast is not a golden rule because I've seen many good foilers with some ahead of the mast and others well behind the mast.. Maybe it has more to do with foot pressure (front or rear foot).. or what you get used to.

I use a similar board and foil set up like you and I always have my mast at either the middle or more often towards the front of the boxes.. The idea is to move it forward for more lift and back for less lift.. So for very strong winds I move mine back towards the middle of the boxes.. (forward=more lift and back=less lift)

I find that my front foot needs to be in the perfect spot on the board and my rear foot can be just were is comfee.. Your foot not being where the footstrap mounts are is common thing in most boards and it can vary from one person to another so if it's not working for you you have to wonder 'is it the board' .. 'or is it you'.. I find the foot strap mount to be in the perfect spot on the board.

mcrt said..
Try this to balance the board&foil combo:
-Post from Kane de Wilde:
www.foilfeed.net/forums/topic/foil-placement/

-And Robert from Blueplanetwith pic:
www.blueplanetsurf.com/blogs/news/foil-board-setup-tips-board-foil-foil-placement-fo/

This will make your gear work together in the most efficient way.
Most responsive and same foot position for float and foil mode.

Go ride it and place feet so weight is evenly distributed when on foil to avoid front/back leg burn.

Remember that the key to balance is the relative position of your front foot vs frontwing center of pressure.Backfoot is more mobile as DavidJohn said.

This works for all foils,using the mast as ref does not.

Once you find a sweet spot that works you can put a front foot marker with indelible pen or stick some eva foam.Takes the guesswork out.

Thanks will have a read.