SkyLight Specified Cubemap Mip not identical

When I use specified cubemap on skylight, the samplelevel result in reflection is not identical with the cubemap mip. I modified the mipLevel to 2 of GetSkyLightReflection() in ReflectionEnvironmentShared.ush to make sure it sample the miplevel 2, and exclude other lighting components to isolate the reflection.

Is this a bug or something? Cause it effects the roughness of PBR a lot.


UE4 Reflection on miplevel 2


CubemapGen Reflection on miplevel 2


UE4 Texture Display on miplevel 2


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