@Wolf,
The screenshot above of caves uses ini settings of
lightmaptexsize=512
lightmapquality=50
So they are pretty standard.
The terrain model you are using is not ideal for lighting it's a twisty devil, it might be one of mine (not sure) if it is, it's part of a set of test terrains I gave out as a bonus with a Skybox pack. That thing would be very difficult to uv unwrap and so I didn't take it to the next step and simply uv mapped it with a box wrap. FPSC likely has a hard time with it, but it will lightmap if done correctly.
When you place a single light in your scene to simulate daylight, most around here go for insane light ranges, I have even seen it recommended to use a range of 3000-5000, which is way beyond the area of the grid space in any direction and even flat surfaces will suffer if not level. The default lightmap attenuation of 16 is ineffective using this kind of distance.
Lights in FPSC are radial only, so when setting lightmap quality I suspect this determines the number of rays cast (as I understand it, I might be wrong). Rays are cast 360 degrees from the light source. The further the rays are cast the further apart they become and quality is lost, so you must increase the texture size and quality aggressively over such large distances.
The screenshots below use four lights with a range of 1000 rather than a huge range single light, its best to use ambient lighting more for outdoor scenes with smaller range lights placed where you really want shadows cast.
The ini settings are
lightmaptexsize=2048
lightmapquality=90
You could also increase the lightmap attenuation a little to soften light/shadow distance and helps hide strong shadows going in wrong direction due to radial lighting, it's a balancing act.
This kind of terrain, if I were to create more of it, would be more modular so it would be easier to properly uv unwrap, making it easier for FPSC to handle when lightmapping it..
I don't trip over...I do random gravity checks.