Any metal detector could hit that ring, provided that the iron bias has enough low end range. Put another way, if what you're saying is true, I'd bet that if the engineers lowered the IB on the Nox, it would hit that ring.
The engineers can make the IB go as low as they want. They can then put the ring and nail on a box, and proclaim how well there detector hits the ring. Heck, they could even lower the IB so much, that most nails would start to identify as nonferrous...and that is the caveat. In other words, everything looks great in the controlled test above the ground, but once in the field, such a low IB would introduce excessive iron falsing.