RE: First runs on F-Type 158 + 11.0
Remember, when adjusting your stance and boom height/harness line length, that the goal is to keep the rig as vertical (side to side here) as possible. The sail is most efficient when it's raked back all the way and standing nearly straight up.
You need to have your body (upper body weight here) "suspended" from the harness lines and your shoulders as far away from the boom as you can reach (even with your shoulders rolled forward a little).
It's simple leverage here. The farther away from the rig you get the weight, the more power you can comfortably handle.
When you get it right and everything balanced and adjusted, your arms will be doing virtually nothing (besides adjusting sheeting angle).
When at full speed, you should be able to "play the piano" with your fingers on the top of the boom. If you can "play the piano" you can't be holding the boom in a death grip and pulling hard with your arms.
As long as you butt doesn't drag in the water, you have enough clearance.
This is quite different than on smaller boards where you stand up quite a bit more toward the vertical and tend to "push down" a little with the back foot.
On the F-Type, your back foot takes about 90% or more of the load, and you may actually be pulling up a little with your front foot.
This rolls the board slightly to leeward, and gets it "up on the fin" where it's able to plane fast and free.
Hope this helps,