We'll let your skills develop, but normally the lines are very short for upwind sailing as
you are "hiked out" to the full extent of your arms length, but leaning more forward with your rig pulled in and raked back fully. This allows you to lean back as far as you can to "cantilever" your weight to the side of the board.
For sailing on a beam reach, or downwind, the harness lines are normally lengthened so you can lean more to the rear of the board and get even further away from the rig.
So, I expect that you are in some sort of "transition" skill wise, and all of these little "nuances" will become apparent as you get more skills and more time on the water.
I agree with Ellen on the waist vs seat harness issues. If you are doing OK with a seat harness and you are not wave sailing or sailing really small boards and rigs, the seat harness gives you the best leverage.
Hope this helps,