By the end of February 2019 Google has announced that its average position ends. It will be replaced by new metrics introduced in November. In Google representative’s words, the new metrics are the best for optimizing the position.
New metrics are Search top impression rate and Search absolute top impression rate. They inform about how your ad was placed in the search. These metrics exist also as shares. Search top/absolute top impression share indicate, whether there is a possibility that your ads will reach the top or absolute top position in the search.
Compared to average position they present an advantage. The average position may not always be decisive, as it showed only integers and those resulted from comparison with other ads. New metrics take into account only real position of your ads in search.
Search top/absolute top impression rate is metrics only about the placement of your ad. It will help you to understand the changes of click through rate caused by the change in the placement of your ad. Google also warns that these metrics should not be used as goals.
Search top/absolute top impression share is a metric that you can use as a target to set your bid to show your ad on higher position. Another close new metrics is also Search lost top/absolute top impression share. This metric estimates how often your ad was not the very first or did not show above the organic search results due to a low budget.
As for now, this information is just an announcement and the first changes should not happen until September 2019. Therefore, you have a lot of time to get to know how these new metrics work and adjust the settings of your ads.