Good point ObiHahn. I think the reason they added the drop boxes on the original costumes, was to cover up the black areas between the thighs and butt-piece. I've also noticed there being almost no gap between the belt and the drop boxes, and to achieve this can be rather problematic, because when the drop boxes touches the belt, it totally restricts further movement, which can make it harder to raise one's legs.
My personal view on this is that the drop boxes should hang as much close to the belt as possible, and that it should be able to cover up the black area between the thighs and the butt. If the drop boxes is attached closer to the sides, one also avoids the drop boxes being restrictive to one's leg movements (for instance when one climbs stairs). I've attached the drop box straps with industrial velcro, which makes it possible for me to do adjustments easily.