Something I've noticed with Facebook ads is that images with higher click through rates have higher associated CPCs. Shouldn't this be the opposite? After all, Facebook says they reward you with lower costs for having more relevant images/ads (of which click through is a proxy).
For example, this simple ebook cover test we are doing. The image on the right has a higher CTR but also a higher associated CPC and higher CPM (Cost per thousand impressions).
The goal of the test is to use the cover that performs better. By CTR that would be the one on the right. But by CPC and CPM that would be the one on the left. And so things are murky.
Why is this Facebook pros?