First, in this case, sample is so small that noise dominates.

On your main questions, yes, established apps with known average-beating clickthrough and (where possible) targeted demographics are matched to higher-paying-per-click lower-volume advertisers.

This is done to optimize total revenue through the network, and to avoid showing all the impressions of a high-paying advertiser on a junky "back page" that has low CTR and low spend.

Now, if you are a "brand" advertiser who values impressions and not clicks, you might be happy on the free back page.