Exactly, you would want to have your skysphere, Sunlight, Skylight, Water level, etc. (everything that should be visible from all world cells ) in your persistant level, not a sub level.
Persistant means it’s always loaded and your loaded sub levels are added to it.
Level bounds are automaticaly stretched (unless you deactivate the option) to fit the objetcs which are in your current sub level. So if you move an object from your current level far from this leve tile, your level bounds will be streched all over your world.
Remember to always set the level as current level when you add object to it.
If you need to move an object from a level to the current level, select it and use “Control+M” shortkey