Ad Auction

The ad auction is like a traditional auction, the more advertisers bid to appear on your inventory, the higher the competition for your ad unit, and so does revenue.

Because it's an auction, AdSense determines bid winners based on the highest actual bid submitted. This true bid takes into account any adjustments AdSense may make to advertiser bids to optimize the auction. If your publisher is still having a headache about revenue decline, you can try this feature on AdSense

In Content Ads - Best Practice

300×250px — Medium Rectangle
728×90px — Leaderboard
320×50px — Mobile banner

These 3 sizes are very popular in programmatic due to high demand by advertisers and because they yield higher CPM.