I would say that when wearing armor over top of NAR, that you should increase the maneuver penalties (both minimum and maximum) for the armor by 50% (rounding up) because while the NAR does not have any penalties in and of itself, it does represent thicker skin or built in scales or plates, and wearing armor over that is likely to restrict movement more than over just plain skin.
So, using a 50% increase across the board would allow for combining while still making it at least somewhat balanced through the increased maneuver penalties.