An example of harness line position - Yesterday I was out on 6.0 Maui Sails Switch on a HiFly 105 in winds up to 25 knots. I put new harness lines on the boom and had them too far back (constant pull on the front arm). In this situation, there is nothing one can do to make it comfortable except hope for a BIG gust to balance the rig or stop and move the lines forward. I moved the lines.
If the lines are two far forward, then the back arm has too much pull, so you can sheet out and re balance the rig, but you will lose power and will go slower. You can pull in to add power and go faster. For me, this is better than having the lines too far back.
Balanced is still the best way to go.
If you are trying for a personal best, you need to be well overpowered, which means that part of the time you will likely sheet out to gain a little control in the gusts and sheet in to add power and accelerate when you feel stable. If the winds are steady, the sail will remain somewhat fixed in it's relationship to the board.
As you head off the wind for maximum speed, the apparent wind (combination of wind direction and the board moving through the wind) changes, this is why the sail will not be sheeted in tight to the board, but will be about 30 degrees of the mid line of the board for maximum lift.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.