Google uses an auction system to rank the ads and decide the Cost per Click of each ad. … Higher the ad position means higher the Quality Score and higher Quality Score always lowers your CPC. The ad rank and the Quality Score are interconnected. A rise in Quality Score leads to a rise in Ad rank and vice versa.
For More Information Please Refer: https://medium.com/@dineshsem/what-all-you-need-to-do-to-reduce-high-cost-per-click-in-adwords-79f895c7563a