First off, I have never honed with a j-nat and find them and their terminology very confusing.
After reading all this I can remember years ago talking to the guy that was mentoring me about them.
He told me that I would be better off if I stayed away from them.
He said that in all his years of honing he had to buy five of them to finally get one that worked right.
Sounds like you might have just gotten the wrong stone.
I know that there are boatloads of guys that use them and love them. I would consult with someone that knows them inside and out before picking out another.
Just my 2¢
Good luck Gerry!
Pete <:-}