Experiences w/ Admob
Over the past year, I have played around with monetizing an iOS app with Admob. In that time, I've grown the user base and thus daily impressions. At one point I thought that if I kept acquiring more users I would also make more but that's not the case. Yesterday I had a record high for impressions and a near record low for impression RPM. It seems that as the daily average impressions rise, the daily average impression RPM falls.
I've tried mediation with Facebook ads but the impression RPM for them was really bad for the few weeks I used it.
Has anyone had a similar experience to this or have suggestions on how to improve it?
I have a handful of apps that I monetize with Admob, and my experience has similarly been all over the map. As far as I can tell from a few years of data, the CPMs are almost entirely dependent on the click rates on your ads. Increasing impressions won't help your CPM unless coupled with increased ad engagement (increasing impressions alone seems to have the opposite effect, as you've experienced). Increasing ad engagement can be tough, though. The only success I've had on that front is changing when ads appear (between actions taken by the users instead of every X seconds).
Which ad types are you using in your app?
I'm using a banner per screen and a single interstitial after an action. I used to use a different banner unit per screen and I'd consider doing that again. I've tried to find a correlation between impression RPM, impression CTR, and the number of impressions but there doesn't appear to be any as far as I can see.
Your CTR isn't correlated at all with your RPM? That seems really strange to me, but that's just based on my own experience. I'd think CTR is the primary factor affecting your RPM.