the lightmap uvs are shown here: https://imgur.com/a/S3rav. it’s all flat planes. no thickness.
yes the floor looks fine but the wall that is in direct line of sight to the emitter looks pretty bad (in situations with emissive light coming from the ceiling that means that the floor would look as bad as that wall. it’s almost as if the result gets worse with increasing attenuation. and it’s probably not a light bouncing issue since this appears in direct LoS as well.
thanks for suggesting portals! that gets rid of all those issues. so that basically means that most emissive light source objects require a portal in front of it… I previously thought portals were only used to get sunlight focused properly in interiors. hopefully unreal can cope with dozens of portals per room for localized lighting. will have to test this
thanks for all the help!