Sets the size and height of the horizon. By default the size is 4.0 and the height is 0.0. This affects how high the horizon color extends before becoming the sky color. The height value is in world coordinates and everything at or below this height will be the horizon color. Above this height the horizon is blended into the sky color until at a certain point only the sky color remains. The horizon will always be at the specified height in the world, even if the camera moves up and down. The size value is not relative to any world units and needs to be set to your liking, then effective range is from 0.1 to about 50.0, but can be set higher. If the view range is small then the height value will appear to have greater effect as the sky box is drawn closer to the camera than if the view range was larger. For example a horizon height of 100 with a small view range will appear very high, but when the view range is larger the camera is viewing the horizon from much further away, so a height change of 100 units will have less effect.
SetSkyBoxHorizonSize( size, height )