The mouth of Sauron has spoken

[Anomalocaris]

Doesn't the ring call to Sauron?  If he only had to concentrate on one group, nine would be adequate.

if it calls to sauron in a way that allows sauron to always home in on its location,  there would be no story.

apparently the nazgûl could only vaguely sense the proximity of the ring unless someone actually put the ring on.   even if the ring is put on it does not allow sauron or his minions to pin point the ring’s location from afar, else sauron would have had large number of opportunities to track down the ring while Gollum had it.