First, one needs to differentiate between the eCPMs of each segment - eCPM for each placement, per date, per GEO and per campaign. Meaning you can have a nice overall eCPM but one of the GEOs may take the average down. For example the eCPM in India can be low compared to the U.S.
If you would like to increase the overall performance please create a new placement ID per each one of the events you are showing Appnext ads within your app or site.
Make sure to use Appnext's most recent version of your desired tool.
For best performance as proven by thousands of developers and years of experience, showing our interstitial at launch of your app or site will generate the best results.