The mesh is one-sided without thickness.
As for volumetric lightmap samples… They are such a headache! They never work as I want them to. I can’t control them - the engine just does whatever it wants. I lowered samples cell size down to 75 even, and it’s still not working properly. I have lightmass importance volume around the area where I need proper lighting. But the engine still places a lot of samples above my interior, where they are not needed, and doesn’t place enough samples in another areas inside the level.
See how it simply refuses to put any samples in this area for some reason? Between the end of the stairs and where the camera is.
Or this tile completely lacking any samples.
But I had a separate thread about this exact issue : How to prevent character and movable objects from being highlighted through walls? - #17 by Kligan