RE: Harness line position - larger sails
I did the same with my 8.5 Severne OD.
It feels strange in the beggining but if I´m not wrong, Guy himself says that you´re not supposed to be super comfortable and that there will be some pull at the front (mast) hand. And so it is, in fact.
I guess that it also might require some ajustment in your stance as well. You´ll be more square to the board. So, why don´t you try to see if a little different stance doesn´t make you feel more comfortable?
Using Guy's method I felt that I get less tired and a bit more in control.
Other than that go with what Geo said.
My two cents.