Lightmass Importance Volume

I just found out that even I set the Lightmass Importance Volume so small only include part of the map. Every in the map still generate lightmass

The lightmass importance volume only helps UE to calculate the lightmass information much quicker in this volume, it doesn´t bind it to the volume. If you don´t want to have an object baked you will have to set it to moveable.