Hi Paul,
I used to fly one ofthese... nice kite!
The different settings are to give you more or less bar pressure apparently but a pro who used to fly the GK's reckoned there was only one sweet set up so here it is below.
F3 & F4 on the front lines and B2 on the back lines.
I flew it like that all the time and had no complaints.
Start there and then experiment if you like later.
Cheers,
Rory
Work to live... life is too short