The Ezoic system will test a combination of ads - both above the fold ads as well as below the fold (and within the same user session). 

The placeholders you create and the goals you set in the UI will influence the types of ad positions being tested.

Google's actual advice on this is that they judge above the fold ad placement on a site basis, not on a page basis, and "affects sites that...load the top of the page with ads to an excessive degree". Because we are constantly balancing user experience against ad income, we could not reasonably fall into the category of 'excessive'. 

We test above the fold ads if a) revenue is deemed to be an element of success for the publisher, and b) we are adding value to the user by improving overall UX.  

We have done many tests both with and without ads above the fold for several years. All the data points to this being just one of many factors that Google uses to determine user experience. The key takeaway from Google themselves is as follows:

Overall, our advice for publishers continues to be to focus on delivering the best possible user experience on your websites and not to focus on specific algorithm tweaks. This change is just one of the over 500 improvements we expect to roll out to search this year.

For more information:

 http://googlewebmastercentral.blogspot.com/2012/01/page-layout-algorithm-improvement.html