[Mithadan]

We do not know the "range" of osanwe. We do know from the essay that one factor allowing osanwe to be possible is the openness of the recipient to receiving the message. Another factor is likely the native strength of the sender.

We do know, or can at least assume, that Gandalf employed osanwe when reaching out to Frodo on Amon Hen ("Take it off! Fool, take it off! Take off the Ring!"). William would be better able to quickly determine whether Gandalf was on Caradhras or in Lorien (or being carried by Gwaihir) when this took place, but this transmission was from a distance. We can assume that Sauron, a Maia like Gandalf's message to Frodo, could similarly transmit his thought to a Nazgul at a distance.

Then there is the factor of the recipient's willingness to receive the transmission. A Nazgul, under the control of Sauron who held the Nine, would be entirely open to receiving a message from his master using osanwe.