Issue about House Ads Campaign on AdMob

Hi,

I have done 3 weeks ago a House Ads Campaign in AdMob for a landscape app based on my own interstitial images. I chose Image Ad, and I uploaded 2 interstitial images (1024x768 and 480x320). After that, languages: ALL, All countries, all devices, and I chose and impression goal, adding all the rest of my apps as ad units (only the interstitial units, since the campaign was only for interstitials). The number of impressions of the “impression goal” was big enough to cannot achieve in the campaign (5 days), so all the rest of my apps were showing only my interstitials.

The result was that the sum of “home ads” impressions and “other advertisers” impressions did not reach in any day the impressions of the same day of the previous or next week, so I suppose that something was wrong. Any suggestions? Should I have uploaded other size images?

Thanks in advance

Please, any help?