The thing with INFJs I found is that we are highly variable. For me, I'm mostly in the background quietly observing things unless I spot problems or potential problems. Then I step in to help sort things up, provide new perspectives, different way of looking at things. Very one on one type of help. After things are back on track, I leave. On the whole it gives the impression of "nice but detached".
INFJ guys... I only know of one... he's not easily typed unless you're an INFJ yourself or know us really well. Again, look for that Ni. It's good to throw at them something random... like an Ne idea. See how they deal with it. Switch topics halfway and see if they're still thinking along the lines of the first idea (tying the first idea with the 2nd etc) or follow you strictly onto the new one. That's the best test for Ni vs Ne.
INTJ vs INFJ... just look for the sentimental side.