I noticed something else! I always fly with 50% zoom! If I fly with 100% zoom then buildings apear earlier, not so late like 50% zoom! But is the ONLY ONE scenery that has this problem
This is not "a problem". This is called LOD and, fact this is the "only one" scenery that has this "problem" ( which is not a problem ), it's because not many sceneries use LOD to optimize fps, because it takes extra effort to do it so, most developers simply don't bother.
LOD is dependent on a combination of your screen resolution and your zoom setting so, the less resolution you have, the earlier the objects will disappear, since the values are calculated from the size of an object in Pixel on your screen, not its distance from the observer.
Of course is better to fly with 50% zoom to have wider view and more crispe textures!
Of course not. Using wider zoom to increase the resolution it's just wrong, the proper way to get sharper textures is to use Anisotropic filtering and, by flying at 50% zoom, you are altering the perspective and the relationship between far/close objects.
It's commonly accepted that, in FS9 or FSX, the most realistic zoom that matches what you would see in a real cockpit without altering the real perspective it's around 70-75%, so we usually optimized our sceneries for that.