If you look at pictures of the second Death Star, you will see that most of its mass is located closer to the superlaser's emitter dish. This was pointed away from Endor toward the Rebel ships at the time of the exposion.
* The explosion came from the main reactor at the center of the sphere - not from the center of mass. This means that most of the Death Star's mass (80%?) must have been hurled outwards, away from Endor.
* Because the Death Star was orbiting Endor, it is reasonable to expect that a good portion of its mass after the explosion would continue in the same orbit.
* The force of the explosion would reasonably launch debris into new orbits around Endor.
* Some debris is not moving fast enough to orbit the moon, but will eventually land after a long time after at least a quarter of a revolution over the moon. Much of this will fall on the other side of the moon from the Ewok village.
* Remaining debris pointing towards the planet will be spread evenly towards the entire hemisphere of the moon.
* Only a small portion of the total debris will fall over the location of the shield generator. This debris originates mostly from the Death Star's equator. I estimate that this remainder would be less than 5% of the station's original mass.
Remember also that the Death Star despite of its size consists mostly of empty space.