Hi,
Thanks for your reply.
Sorry I wasn't actually clear - my fill rate from my ad server is 100%.
I'm partnered with Blinkx Media (http://www.blinkxmedia.com/) and now that I'm serving ads in friendly iframes my fill rate of paying ads has dropped to 20% and Blinkx Media are passing the ad requests over to my in-house passback ads - I hope that makes sense.
According to this blog post from monitize more - they've experienced a similar problem as well (http://www.monetizemore.com/blog/are-the-new-dfp-ad-tags-gpts-decreasing-your-ad-revenue/).
For some reason, even though the iframes are on the same domain as my website (i.e. firendly iframes) they are still affecting real time bidding ad revenue. Maybe advertising are not getting the info they need or something - I'm not sure.
It's really hard to balance performance with ad revenue.
I realise this is a tricky issue, but I'm really not sure how to proceed - its amazing to have a community like this to turn to.
Thank you for all your help and thoughts.
Ben