The reason I use the GFZ sky there is because I'm using the other sky that would fit there already, cloudy, way too damn much as it is. Personally, I think that sky really sucks, and only use it because I have to. Also, if I changed the sky in Flame Rift to something else, it would have to be off of full-bright, which would be hard with so much lava to be a light source. I'd personally like to use a red sunset sky there if I can get one, but for now it'll remain GFZ.