I think it's not that much the mast placement on the fuselage (closer or further away from the front wing), than the minimum required length of the fuselage that's important for making the wind foiling setup comfortable to ride. Ca 90 cm fuselage (measured from the leading edge of the front wing until the end of the fuse) is quite optimal for wind foiling, and going way shorter into 65 or 70 cm range (like the wing foil fuselages mostly are) makes the ride quite a bit more nervous. Possible to get used to for sure, but you'd need to put some time in.
I have tried the MFC Hydros setup with a sail. While a sweet foil with a wing, it was not easy to wind foil with that. The first things you'll sacrifice when trying is the low wind comfort of riding, and the ability to go faster. Better to have plenty of wind, with a small sail, go slow and get used to the nervous feeling, and then report back how it felt.
The final comfortable foil placement was a bit further forward than on that picture.

I am sure some other front and back wing setup might work way better when used with a short fuselage. Some wider stabiliser for example, and a front wing that's not so agile and willing to turn all the time as the Hydros.