I read a comment on this forum recently "most newbies have their harness lines too far forward". I've since moved mine back a few cm and it does seem to help being powered up in lighter winds. Checking harness placement of some videos of sailing in light winds here, I've noticed some of the gurus have their harness lines so far back they're closer to the back of the boom than the front. Maybe that's how they get the sail so closed up against the board.
The only guide's I've ever been given for harness line positions are:
stand the rig up on the grass and find the neutral position along the boom where you can balance the sail
measure one fist back from the front of the boom for every metre of sail
Do these only relate to windsurfing? i.e Should I set the harness lines much further back for foiling?
I would say no. My harness lines are in the wrong spot when I need to become heavy with front or back hand.
Early on there was a suggestion that moving the lines forward for foiling helped beginners. It certainly helped me heaps because I could sheet out more easily and prevent a breach with the lines more forward. As I got better I learned to control a lifting foil without sheeting out.
For the past two years my lines are in the normal spot.
My trick is simple, get up on the foil, hook in, let go of the boom with your hands.
>If the sail falls forward move your lines forward.
>If the sail falls back move your lines back.
Do this in average wind, maybe slightly below average, you'll be able to move your hands a little in gusts and lulls.
Select to expand quotethedoor said..
I would say no. My harness lines are in the wrong spot when I need to become heavy with front or back hand.
Early on there was a suggestion that moving the lines forward for foiling helped beginners. It certainly helped me heaps because I could sheet out more easily and prevent a breach with the lines more forward. As I got better I learned to control a lifting foil without sheeting out.
For the past two years my lines are in the normal spot.
+1
Select to expand quotethedoor said..
I would say no. My harness lines are in the wrong spot when I need to become heavy with front or back hand.
Early on there was a suggestion that moving the lines forward for foiling helped beginners. It certainly helped me heaps because I could sheet out more easily and prevent a breach with the lines more forward. As I got better I learned to control a lifting foil without sheeting out.
For the past two years my lines are in the normal spot.
+1
Select to expand quotethedoor said..
I would say no. My harness lines are in the wrong spot when I need to become heavy with front or back hand.
Early on there was a suggestion that moving the lines forward for foiling helped beginners. It certainly helped me heaps because I could sheet out more easily and prevent a breach with the lines more forward. As I got better I learned to control a lifting foil without sheeting out.
For the past two years my lines are in the normal spot.
+1 and I would also add that the universal position is really importante using HG system at first at use the dimension from the foil academy video and after the one from Wyatt Miller YouTube video and now full back on my wizard 105 and I not playing any more with my harness line same position as on normal windsurfing
When windsurfing, the back of the harness line is 1/3 from the mast. This creates quite a bit of pull on the front hand when slogging, but feels absolutely perfect when powered up.
But this doesn't work at all when foiling - the front hand pulls too much. So I move the lines further forward.
First, I leave my lines slightly loose on the boom so I can do all adjustments on the water by wiggling/sliding the ends of the lines on the boom to move them back and forth (Sailworks Quicktune lines). I get the lines placed on the boom so the sail is balanced with board on the water (that may require lengthening the lines initially, if you run short lines like I do), then when in flight and hooked in I note if I am using constant back or front hand pressure and move lines accordingly (i.e., move lines back if using constant back hand pressure). Now if the wind increases and I outhaul the sail more on the water, that moves the pressure on the sail back and so I move my lines back too. Now I keep both ends of the lines close, about 1" gap between them, if you have them farther apart they will be less sensitive to outhaul changes but that will also make it harder to feel if they are perfectly centered and reduce your ability to sheet out quickly for gusts. Generally, once I get them centered, I only need to move them back and forth ~1-2" for changes in outhaul. Picture is of a 160-220 cm boom, lines are adjusted for a 5.8 sail with moderate outhaul (sail well off of boom) and winds around 12-15 knots.
I move my harness lines around due to my sail shape. For me, I want balanced hand input. However, the faster we move through the air, the lift on the sail moves rearward a bit.
I forgot my harness and had no choice but to "foil-on" without it. I ride on big wings (Moses 1100/790) and small sails (5.5m->3.6m).
After a 3.5 hr session in 15-20mph I was kinda sore, but didn't really miss the harness...
The following week, i foiled with my harness and found that I used it less....cause I knew I could. 
Next I went strapless...found out that no harness and no foot straps, I could move quicker and easier and could maneuver around chop, boat wakes and gusts. I made more foil gibes and now have hope for a 360.
Less is more?
I rarely use a harness for freeride foiling. If I want to crank hard upwind, yes, I use the harness then. Otherwise, you don't need it.
In gusty conditions, a harness is actually a liability. Too hard to make sail sheet adjustments when hooked in.
