Mike, the way it was explained to me is that well of influence decreases as you move away from the rod as a function of the square of the distance. At 6 feet the effectiveness has decreased enough from the first rod that there is an effect from the second. I do agree farther is better but rods are simply a poor choice in the first place.

Very True....just that driving a 2nd rod 6ft from the first is useless for lowering grounding resistance..but meets code.