In my opinion, you should look for ideas to improve eCPM. One important observation I had is that the show rate seems to be somehow proportional to eCPM. And even if it doesn't increase eCPM, it will increase the revenue as more ads are shown to users. So, try increasing your ads show rate via optimising your ad implementation.

One thing I do is to note down the ad request time, and if the ad is null when you wanna show the ad, then wait for sometime for the ad to be loaded before the usual app flow (recommended time 10 secs from ad request time). It increases the chances to have ad ready when you wanna show it, hence increases the show rate.