Agreed. Also, what is the actual iPhone app? Where was the ad(s) placed? Different kinds of apps will have different ctr. And ad placement is also very important.
Without context we can't validate your claims and hope to reproduce them. Thanks.
The 0.1% CTR apps relate to mobile games where there is little interaction with the ad is 'Word Seek Social Lite' The 4.5% CTR app relates to generalized RSS readers similar to FMyLife (ex: Softbaum's FMyLife for which we have a rev sharing agreement).
Hope this helps, of course since these are highly profitable, I can't share too much details.
It's great to share, it's better to explain. Thank you.