Mixed lighting on multiple scenes

Hi everybody,
we have a large terrain (3X3km) scene. We split it in 4 parts and four different scenes to improve editing performances and help the generating of the lightmaps. Obviously we have static and dynamic objects and we use mixed lighting mode.
Now, the problem is that after we generate lightmaps separately in every scene, we import them all in a new blank scene (MAIN SCENE) but the directional in the new map affects static objects too.

  1. We try to set the light in every scene as baked and it works, but we need a mixed light in the main scene and it affects static objects too, which it should’nt do…
  2. We try to set the light’s culling mask in every scene (working with layers) and it works but when a dynamic objects moves from a scene to another it stops to cast shadows (forgive me, it’s hard to explain…)
  3. The only thing that seems to work is generating the lightmaps in the main scene all at once. But the PC goes always out of memory.

Anyone has some tip?
thanks to everybody!

Did you find a solution to this issue?