Turning off the Enable Ground option still leaves this haze layer. I agree with you, it would be real nice if turning it off would provide sky from top to bottom.

I have also played with the Horizon Altitude, going from the largest positive value it would accept to the largest negative value it would accept, and saw no difference at all. It does not seem to have any effect.

The only alternative I could find was to do what you are trying, tilt the scene and camera towards the sky.