LOD_RADIUS IS KING
We have created a page with the most important advice for getting the highest resolution and clarity for your MegaSceneryEarth scenery. It's all about the FSX Setting LOD_RADIUS=??.
FSX default maximum is 4.5. This was deemed appropriate when FSX was originally released but with today's powerful PC's you can comfortably support a higher value. It results in a much higher resolution scenery around your aircraft and into the distance. The thing is that you need to manually set a higher.