Navmesh volumes and level streaming

My game entails a large, sprawling environment made manageable by breaking everything into tiny levels and using streaming to load/unload them as appropriate. I’m a bit confused on how nav mesh volumes should be employed in this case, however: is the intended use a single, giant navmesh in the persistent level that covers the entire world, or tiny volumes in each sublevel which are barely large enough to cover the traversable space inside that level alone?

Bump - anyone got any suggestions about this ?