having flown a scenerio using real weather,over the south of France with a overcast sky between 4,500 feet and 6500 feet, using orthoscenery with autogen and a few other ground improvements, i was getting around 35-40fps below the clouds, i then climbed to fly above the clouds, no land visible and only had 16-18 fps, mystified i then descended to below the clouds again and straight away had 35fps, how can this be? when above the clouds i tis only painting clouds and sky yet below it is painting everything in 3d virtually, is this a bug? I would really like to know please