One of the problems with Bryce textures, skies, etc. is they are built on an X,Y,Z axis. Your fog plane in skylab will go straight even if the ground curves up. The easiest way to get around this is just model a flat landscape then use a fisheye filter in a photo editor and layer the image as a background.

If you want to model a curve then you should turn off haze and fog and use color perspective instead. You can add or subtract Red Green and Blue to the image with distance from the camera. For example 5 red 5 green and 5 blue make the scene go white with distance. This is great for snowscapes or rain but should also work for your situation as well.