The sky entities never worked properly. They always overlap geometry. I would use a 2nd view, behind the actual camera, and syncronize both views (pan/tilt/roll). The advantage: you can place any entity in this "background layer", and they are ALWAYS in the background. You only have to place the 2nd view (+ the background entities) somewhere, where the normal camera can't look at (a few thousand quants above/below the actual level).