Lightmass importance volume

Hi

Do the LightmassImportanceVolume shape must be box ? I’m asking couse my levels ale mainly L shaped or U shaped (with hollow interior). Would adjusting the volume to tightly encompass level will have any positive effect ?
(there is no geometry in the hollow interior of U shaped level (think of it as a U shaped pipe with the rich interior and absolutelly no geometry outside (this is a closed racing track)))
Thanks for definitive ansfer ansfer.

You can use multiple importance volumes.

If there isn’t anything outside the importance volume, changing its size doesn’t matter.