If the main deflector is a less powerful shield projected thousands of kilometers ahead to sweep small objects / meteors / debris out of the path of the ship, and they are weaker than the combat-rated deflector shields, why would a ship use them to the rear? Does that make it harder for fighters, shuttles, and small ships to approach from behind, in the region with less direct firepower? Or is the rear dish perhaps a means of reinforcing the regular shields, and does not project a weaker field farther away?