I am not sure how I missed this, but in March, the AdSense blog announced they are testing "above the fold" ads for advertisers. Google said:
The new feature enables brand advertisers to target their ads to ad units that are immediately visible when a page is loaded -- in other words, the portions of the page a user can see without needing to scroll down. The ads that are immediately visible are called 'above the fold'; those that require a user to scroll down in order to be seen are called 'below the fold.'
How does Google know what ads are above or below the fold?
In order to determine which ads are above and below the fold, we've implemented a statistically-driven model. The model takes into account various user experiences and situations, including different web browsers, monitor sizes, and screen resolutions, and only considers ads above the fold if they are fully on-screen when the browser window loads.
So advertisers in the content network can exclude below the fold ads by following these steps. These steps only work if you have campaigns targeting the content network and you are in this test:
(1) Click the Campaigns tab. (2) Select a campaign. (3) Click the Networks tab and scroll down to the bottom of the page. (4) Click the Exclusions link. You'll see an "Ad group level" table and a "Campaign level" table. (5) Within the Campaign level, click the Add exclusions drop-down menu, and select Exclude category. (6) Select the "Below the fold" checkbox, and click Save.
Forum discussion at WebmasterWorld and Google AdSense Help.
