Not really. It's been my experience that it is on par. They have content that's why. When people are interested in the content they read on and look around later so it works better towards the end of the content. If the content is uninteresting or the content owner is looking for the quick click then the ads work best on the top. It's because it's not worth the time for the surfer to hang around and the content owner doesn't really care if they do anyway.