i just found out myself helpless when i changed the ad type in my app from banner to interstitial. But i used the same ad-banner id from admob. though the interstitial are appearing just fine, my ecpm is quite low....
i tried to edit admob adunit type from banner to interstitial for my app but it is disabled under my app setting tab.
so do i have to create a new adunit id for my app and post the new version of my application in the App Store with updated ad unit id?
Short answer - yes.
You need separate AdunitIds for banner and interstitial. They pull from different pools of available advertising.
They are also presented differently on the client. You need to use different APIs to present interstitials than banners. See https://developers.google.com/mobile-ads-sdk/docs/admob/advanced
来源：https://stackoverflow.com/questions/20643467/how-could-i-edit-admob-adunit-size-from-banner-to-interstitial