We understand it’s valuable to know how prominently your ads show on the search results page. So, in November, we rolled out “Impression (Absolute Top) %" and "Impression (Top) %”, which describe what percent of your ads appear at the top of the page and absolute top of the page. These new metrics give you a much clearer view of your prominence on the page than average position does.
To complement these metrics, we also rolled out "Search absolute top impression share" and "Search (Top) IS". If you want to optimize for position, these are the best metrics to use. And you can use the Target Impression Share Smart Bidding strategy, if your goal is to get your ads to a prominent location in the search results.
With the availability of these new metrics to understand prominence, we plan to sunset average position in September of this year. If you currently use average position, we recommend that you start using these new metrics when measuring and optimizing for prominence.
Source: Google