Richard, The top rollers are eccentric cams so you can raise or lower either end of the door. They also adjust in or out to get the necessary geometry to keep even tension on the bottom guides as they open and align the door with the magnetic strip just as it closes.
You need to stow the door in the open position in transit because that is where the strength of the glass is supporting the weight of the door. If you step back and look at the upper track in the center, you will see where it has bowed downward from the weight of the door. They do not make replacement parts for this door so be careful. Fred