Matched requests show the number of requests where buyers were matched with the ad requests. Improving the matched requests can ultimately increase the number of impressions served on the website. The number of matched requests can be higher than the impressions because sometimes the ad exchange can fail to deliver impressions to the matched requests. Tapping on the larger demand pool can improve your match rates.
You have to figure out the ad sizes with least demand (see the impression data for the sizes) and enable multisize ad requests for those units. For example, we have started to observe that 728×90 ad size is getting the least demand. Multi-sizing the slots to make way for 300×250 ads has increased the matched rates.
We have also observed that some publishers block many categories to show only relevant ads on their sites. If you have also blocked any categories or specific advertisers, then temporarily unblocking them can increase the matched requests.
Last but not least, we suggest you go through the pricing rules and Protections in Google Ad Manager to ensure you aren’t preventing buyers from bidding on your impressions. Though it makes sense to block certain categories and advertisers, it’s time to see if you can un-block anything.