I guess yeah, even if I think it’s weird to have this cubemap setting inside the postprocess volume. Since almost none of the samples are using this setting (I didn’t check every one of them, but the Shooter game don’t and the Realistic Rendering neither) it would be nice to know a bit more about this.
By the way, the Lightmass documentation has been a bit updated regarding its UE3 version, but I believe there is still some changes to be done