I think that above folks have the best solution.  Unfortunately, the only way to really lower the horizon is in the sky mode (Mark, you may want to step in here if I'm full of hooey) even though both mode show the Horizon Altitude that you can plug  say -22 inches, it works in the sky mode but I can't get it to do squat in the realistic sky mode (yeah, if I lower the puppy to  -3000, I get the Earth's curvature-a nice grey curved surface-at least in Carrara 5 Pro).  Jan