hmm… Might just be me then. Most likely I need some more time to understand UE4 ^^,
Anyways, In unity all objects with a “texels per unit” resolution that is smaller than the Lightmap resolution gets packed automatically into a new Lightmap UV layout. (cross object) so that all imported object gets the same lightmap real-estate. So unless the object is larger than the allowed lightmap resolution, it will get packed together with other object in the scene. (c:
Edit: I was assuming that UE4 packed objects from within 1 FBX export into 1 Lightmap only? Is this the case?