I started with my lines all at the one length, but have now shortened the back lines (by one knot length each) as to give me more power... This is on my 10m Cab Element.. However, when I use the 16 Naish, I have to undo this knot otherwise they are too short, and the kite flies backwards too much and looses power...
Just have a little tweak with your lines, and by the sound of things, you need to make your front lines a tad shorter by either shortening the lines, or by repositioning them when you tie the lines to the kite. All the best mate

Report back on what you find works bedt for you