Reference to the back line or (steering line) knotts on the kite,the knott closest to the kite will give you more power where as the knott furtherest from kite will give you the most depower.
i dont think Xbow2 has knots on front lines so i think you can disregard some of last post.
Also, some of here in the wild west have noticed that the xbow2 does not seem to fly very well when the back line knot is the one closest to the kite or the middle knot, and hence have only been using the knot furthest from the kite. (especially if you are going to unhook)
I have noticed my kites stall on these 2 closet to the kite settings because they put to much tension on the back lines meaning that the kite tries to fly backwards . (it doesn't actually do this but what happens is that the kite might stall as it begins the upward motion of the sine wave)
This means that the default setting is the most powerful one but this isnt a massive problem because there is so much depower in the depower strap and the bar.