Well, if the rears are still too loose, shorten them a bit more. Here's a good illustration of what the kite should look like when properly "tuned" (more below the photo):
Basically, if you oversheet the kite out (pull the bar all the way toward you effectively making the front lines too LONG), the kite will flare out as the rear lines get over-tensioned and it will choke, or stall, the kite. This setting should be known by all, and depending on your riding style (riding the knot, or sheeting completely out during a jump by sheeting the bar in) you can prevent stalling by setting max power at a decent flare, but not over-flared. No flaring basincally means the kite is depowered. If the canopy of the kite starts to flutter, that means you're depowering the kite too much or the wind is lulling. You don't want your rears too long or you can't increase the kite's angle of attack enough, which means the kite will be depowered the whole time, overfly, and tend to stall out. You don't want them too short, either
. Find a happy middle ground. Usually people will tie two leaders one for each rear line and attach them to the kite. Make them 10 inches long with a knot at each inch marking. Make sure they are spaced equally on both sides. Then test each setting till you have it right.
By watching the kite and "knowing" it, you can really tune in to the power of the kite. These techniques can really be used for any kite on the market. Every kite will flare out at stall. Every kite will overfly if the rears are too long.