In my experience, they still find it if the person is chained to me at all. Is this correct? Or am I just inattentive to what character they're talking to? My friend has verified this, but I'm not so sure anymore, after trying really hard to test it out. Are unchained characters an exception?
I said "across the map". If they're chained to you, then they're right next to you, and so it would indeed be good of the NPC to search all of you who are together.
