the component uses world 0 as its sea level, so if you had a 800km ground radius and a 1km static mesh sphere, then you have to move the mesh down by -800km and scale it up by 1,600 km to match radius.
There does seem to be a obvious POP when it switches to fast distant sky rendering from aerial/ ground view. when its in the ground view the atmo border is very obvious. You can use "r.SkyAtmosphere.AerialPerspectiveLUT.Depth " with some big number like 256 to blend it better, the number you use will depend on your planet size
Aerial samples seem to get distributed based on atmo height and Rayleigh Exponential distribution, greater the height the more noticeable the depth stepping "r.SkyAtmosphere.AerialPerspectiveLUT.DepthResolution " will increase the res.
