In an attempt to improve the quality of ad results, Google is adjusting the way your actual cost-per-click (CPC) is determined for ads in top spots. Instead of considering your actual CPC, Google will consider your maximum CPC bid to give you more control over achieving top ad placement. As a result, you may see a change in the average number of clicks and average CPCs for impacted ads.
Google suggests you check your stats regularly and provides some quick tips regarding the new top ad placement formula.
