I've used NR on triples for years without a problem. Is it not shifting to the smaller or the larger? If smaller, try releasing the cable, adjusting the stop then reinstalling cable. If pulled tight, then the inner stop moved, it will never move in any more because the cable tension is holding it.

I setup height with about 1/8" clearance to the larger chainring. Align the cage to the chain in the center position on the freewheel on the inner ring. Spin slightly from there if needed.

Could be the spread of the chainrings. I'm running a couple 28/42/49s with no troubles.