done

Skybox is a 12mb dds that compresses in 7zip to 6mb. The majority of the filesize is taken up by high resolution diffuse texture and normals. The high-res diffuse is mandatory, the normals are not.

You will see skybox reflected from top-down even if not looking up on areas of maps that use skyreflectmod texture like the upper areas of this map. It can heavily affect reflections on units as well.