Admob account showing big difference in matched requests and impression due to ad preloading

Question

Admob account showing big difference in matched requests and impression in interstitial ads as shown in the picture. (The last two rows).

I think this happens due to

Answer 1

This is normal and you are right: it happens because you are preloading interstitials. A good benchmark for impressions is something near 50% of the requests. The first one you preloaded is shown preferably in the beggining of the experience and the second one probably will not be shown leading to 50%. Some ad networks doesn't like preloading with low rates but to Admob, as far I know, the only problem is if you preload more than one ad because you could be doing that to choose the best one.

Answer 2

This is normal. The difference is because there is not always an ad available (an impression) when a request is made. THis can be because of device, locale, time of day, time of year, advertising budgets.

The best way to ensure you always have an ad available to show is to use mediation and have 2-3 advertising networks in your mediation list.