FrankT:  the Vue manual says:

"Aerial perspective: This setting controls the overall "thickness" of the atmosphere. A value of 1 corresponds to the typical Earth atmosphere. If you increase this value, the effect, in terms of atmosphere, will be like increasing the scale of your scene.
In the preset atmospheres, this value is usually set to 10, so the effect of the atmosphere can be seen without having to use "real world" size environments. If you are looking for physical accuracy, you should reset this value to 1, which is the aerial perspective of the Earths atmosphere. You should also construct your environments at Earths scale (hundreds of miles)"

Maybe the term "thickness" is misleading. It does not mean "density" but rather "height".

I guess the reason why the haze appears to be denser is because, if you downscale the atmosphere by going from AP 1 to AP 10,  the same amount of dust particles are now squeezed into a much smaller space.

http://www.eonmusic.ch http://www.artmatica.ch