Erik Loots I have heard that’s some dedicated Speedsurfers are using tow pair of harness lines or different starboard und port settings depending on the wave direction. I personally use cheap vario harness and get annoyed by the slipp trough:)
True, I the past I sometimes swapped gear with very fast speedsurfers. Some use shorter harnasslines for upwind (I also sometimes do this). Some move harnasslines more (up to 10cm) to the back on the boom for the downwind reach.
However there are also very fast speedsurfers that do not use different harnasslines lenght/position for upwind or downwind. It is personally and depends on gear. There was once for example a very fast speedsurfer with always a very high boom position, he changed boards (another brand) . He tried everything, eventually he figured the boom position needed to be very low for these boards to go fast.