Plunge into the path C:\Documents and Setting\
*your account's name*\Application Data\Microsoft\FS9\ make a backup copy of and then open FS9.CFG for edit.
Be careful that your active "
Application Data" folder may have the same name translated into your language, as it happens on my Italian localized Windows, where it's called "
Dati Applicazioni".
Go under the
[Terrain] tag and delete everything under it, swapping it with the following lines:
[TERRAIN]
TERRAIN_ERROR_FACTOR=100.000000
TERRAIN_MIN_DEM_AREA=30.000000
TERRAIN_MAX_DEM_AREA=100.000000
TERRAIN_MAX_VERTEX_LEVEL=21
TERRAIN_TEXTURE_SIZE_EXP=8
TERRAIN_AUTOGEN_DENSITY=5
TERRAIN_USE_GRADIENT_MAP=1
TERRAIN_EXTENDED_TEXTURES=1
TERRAIN_DEFAULT_RADIUS=9.500000
TERRAIN_EXTENDED_RADIUS=9.50000
TERRAIN_EXTENDED_LEVELS=5
Takes a little more power from both CPU and GPU, but in nowadays hardware (
or the one of four years ago, for that) the different drain of resources is negligible and hardly ever noticed.
If you want, you can simply substitute the values of these following lines without swapping all the whole of it...
TERRAIN_DEFAULT_RADIUS=9.500000
TERRAIN_EXTENDED_RADIUS=9.50000
...as they are the ones that control the main aspect of your problem, but I'd suggest you adopt the whole of it, as its performances as a whole have been repeatedly checked with optimal results under all sort of conditions, and if you feel like to return to your previous settings, that's what the backup copy of the FS9.CFG is there for.
Have fun.