In changing the horizon distance, you've effectively changed the sky rendering distance, that is, the area over which clouds will be displayed. You've also introduced clipping.
These are the values I use:
[HighDetailOption]
HorizonDistance=99000.0
DetailMeshSize=6
DetailLevel=1
WaterEffect=2
NoiseTexture=1
MaxTextureRes=2048
Along with:
[FarSceneClip]
FarClipDistance=200000.0
NearClipDistance=3500.0
[NormalSceneClip]
FarClipDistance=140000.0
NearClipDistance=120249.97
[NearSceneClip]
FarClipDistance=120250.0
NearClipDistance=1.2
You may have to set the skydistance in the environment system.ini to a value of 200000 as well, which will also force you to reset the horizon and vertex heights, as well as require you to increase the cloud (count) number for each weather level.
It's almost like Algebra. What you do on one end of the equation has to be repeated on the other end
UPDATE: Here's a webpage with data and graphs that you might find helpful, theoretical distance to the horizon, from varying altitudes ( in meters ):
http://newton.ex.ac.uk/research/qsystems/p...hysics/horizon/