This has been discussed many times on the forum, it's a side effect of the LOD optimization, and it also depends on your screen resolution too. We try to optimize the scenery to work at a Zoom level of about 0.70, which is considered to be the most realistic, and it we allowed to go as far as 0.40, it will impose an fps hit for everyone, even those that use realistic zoom settings.
We are discussing a way to make this user-configurable, which is something we can do, since the scenery is created programmatically, but can't promise any release date for this.