Navigators rarely interact with PCs in my adventures, since they never have enough money for them.
The few times they've appeared, their compasses have allowed them to work whatever destination was required, without the need to be near any specific point.
Also, most of the time this was next to an obelisk, so you'd assume that they were placed in good locations for using transport magic.
As regards Lofty Bridge, I allow it as long as it's for short distances. Using teleport to travel miles by magic will likely leave the party deviated from the path due to the flows. My players know this risk exists, so they have rarely attempted this. If/When they do it, I would do a quick review of a map to decide if there would be a flow in the path that would change the course of the destination. Or I might decide using the flow maps that there could be an Essaence barrier in the way, which would most likely mean the spell fails, and the caster could be stunned for some rounds.
When in doubt about how magic works in Shadow World, I would say that Legacy of the Loremasters has the final say. It was written by the one and only judge of what's canon in Shadow World, and it is one of his most recent works, so it will have the most up-to-date description of how things work in Kulthea.
