I set the directional to 1 lux (low intensity moonlight), and had the sun band. It was when I tweaked the Sky Atmosphere settings that I found lowering Rayleigh Exponential Distribution removed the horizon band of the sun (directional light index 0, the SunSky-inherited directional light) at value 1. It would probably be higher or lower depending on the lux of the directional lights and at least a few other settings in Sky Atmosphere / skylight.
Which makes sense, since rayleigh and mie scattering adjust, how much dust, dirt and other gases are in the atmosphere, and therefore influence the color of the atmosphere and how well the light can travel through it. If there is way to much dust in there (rayleigh and mie set to higher values), maybe because it was built for a light with low intensity, then it would look wrong, if all of the sudden there is a light with an insane (for typical Unreal Engine standards ^.^) intensity values. So we probably have to look up, what values would our atmosphere require at a certain diameter in combination with a certain sun light intensity, to look as we would expect it from daily life.
And we probably have to balance out other values too, that influence the scattering… and there are several of them ^.^
There was another video, where they take a deeper look at Sky and Atmosphere, including Rayleighand Mie Scattering (about 59:24, there is an index in the description and comments):
Oh, they also talk about Moons directly after the Rayleigh part.
It’d be great to get a few SunSky LUTs, but instead of color modding only it would help in choosing values for Sky Atmosphere and light settings to produce particular effects and sky colors.