Grab the top of your upper door, and bend it in. You're going to want to bend the pins where it connects to the lower door. Get it to the point where it's almost hard to close the door. The uppers use a "positive seal" - which basically means they need pressure to keep them closed.
Make sure they're adjusted correctly up and down as well: there should be small "collars" around the pins that control how far the top fits into the lower door. Sometimes if the upper door is too low, it allows a lot of air to grab at the front corner.