My sky looks like that too. I fixed this by replacing it with one of a higher quality and less tilt or Z=xx in the skymap part of the script:

Code:

---

sky horizon_sky {

	type = <backdrop.tga>; // sky image
	tilt = -5; // or z = -5
	flags = scene,overlay,visible;
	layer = 3;

---

This is the code I used and it made the mountains lower. I also got a better image to use, because I run my projects in 1024 resolution. If I used a lesser resolution, the background image appears too big and covers the sky as well. Of course, you can always comment out the whole horizon section and put in a nice sky sube, scape or sphere. It's much more effective than that crappy horizon. Either that or just comment out the horizon and have a turbulent sky via WAD texture. I wish I could only share from my local drive, I have made a nice WAD full of high quality turbulant skies... ah, nevermind. I hope this helps.