Rearward mast position is as said, the safest way to start the very first times where you should only learn to handle the foil and taxi.
Then learn to pop the board free with your rear foot without too much risk.
And then you can move the track forward to better balance.
Also, the brands will recommend this position for safety reasons.
It is somewhat like most brands kitebars comes with rear lines set on the outer knot.
The most safe having max depower, and looks right.
Unfortunately a pretty useless trim for most kitesurfers, so we have to adjust.