i'm no expert but i have a similar but not as serious issue with an ultralight. Widow Maker. in a turtle i have to move back probly 15' to keep the lines from getting too slack. i havent thought much about it since i can stay ahead of it but im thinking maybe the weight of your lines overpowers the weight of the kite. try something like 50' of 50lb line to see if it helps...if the lines youre using are already that light then im stumped (for now)