Design question - Large Environments with many Levels

I have a game area covering 50 sq km with many levels. I currently have most of the generic volumes like navmesh, cull distance, post process and modifier volumes in the persistent level however is it best practice to do this or should they been moved to each level where they are are used ( which would be cumbersome to do). I have tended to keep other volumes such as trigger volumes which are specific to a level inside that level and its blueprint but kept the more general trigger volumes etc inside the persistent level as thought this would improve map loading/unloading especially with the navmesh and paths.

Is there any doco that recommends the best practice or can someone please give any advice as to best practice, especially for things like the navmesh, modifier volumes etc.