You need to EXTEND the backlines ; or keep them as they are but fully trim the bar (to "shorten the front lines , exactly like if you want to depower the kite in high winds); I suppose that with your shortened back lines, kite was almost not controllable , both in turn and in backstall ...
Even if fully depowered, the kite seems to keep its shape very well , without "arcordioning" like most singleskin sometimes do in gust fully depowered..