I don't use the auto-fit either because it is unpredictable, and does not really re-sample the image to fit the scene. It is better to set the U and V scale to something between 1.2 and 1.8 (depending on how wide/narrow your image aspect is) and then use the offsets to position the image where you want it. And the preview window in the Material room does not show exactly how it will render unless it has the same aspect ratio as your main document window. If you don't use the same scale factor on both U and V then the image will be "squished" or "stretched", which can work well for clouds and other images that don't need to be equally scaled horizontally and vertically.