Aloha,
So RPF works both ways, yes the indicator that you are "RPF'd" shows that they know a very general direction you are in, but also tells YOU, you are closest to someone as well, if you're good at reading the map and know common lanes that ships like to drive along, you can kinda estiguess where the enemy ship that has RPF is.
In a division, and especially if I am rolling with another DD, it is actually really easy to start triangulating the enemy ship that is tracking you and prep torps or reposition.
Mahalo,
-Hapa