Like mARC said it's not an easy kite at first and you really should
get used to in in less wind, if it's nervous and too powerfull. Make
sure the brake lines are the same length and haven't ridden up the
leaders, this can ruin the trim. I also found that putting another
knot lower in the depower and trying different trims worked.
The kite will have less power but be more stable except at zenith
where it'll tend to overfly as Mark said if you're using too much
depower or have shortened the depower too much even with the bar at
Mark where the knot is now so you can go back to the original
setting the make another knot about 3cm lower, which will also
shorten the top knot by about 4 cm as some rope is used in the
second knot. Try each knot in lighter wind to see which is best, the
rope is thick and you can move them always, remember that the kite
will fly further towards the edge of the window in light wind and
further back in stronger stuff with the same trim.
If you use the search function for "Mastair" there's loads of old
stuff on the forum.
Have fun and let us know how you get on.