I think Having the ufo always in the same place relative to your craft makes a bit of sense as you would know where it is already if you shot it down. Wouldn't you see it from the sky while landing even if you didn't shoot it down in the first place? I don't really understand having a "fog of war" with the terrain unless the aliens laid down some sort of fog before you land as you would get a birds eye view from your craft upon landing. The player shouldn't know where the aliens are, but I think it's completely reasonable to know where the alien ship is.