iAd : latency and ad inventory issues

I added iAd in my most successful application a few weeks / months ago and I noticed some weird issues.

Latency

I noticed a speed issue : adding a banner to a view, I sometimes gets a response after 10 seconds, sometimes it's pretty normal (like 1 second); I guess it ain't good for revenues since some of my views are displayed only a few seconds, depending on the user. I get this latency issue both on wifi and 3G connections. Did any of you guys noticed the same issue?

PS : most of my users are in France (I don't know if the iAd architecture is scaled for both USA and Europe)

Ad inventory

The AdBannerViewDelegate calls bannerView:didFailToReceiveAdWithError: with the "Ad inventory unavailable" pretty often. I don't know the exact meaning but I wonder if a request receiving this error is registered on 开发者_如何学编程Apple side : since i use AdMob to display an ad when iAd is unable to get one, I have this weird issue of having more requests registered on AdMob than on iAd!

Thanks for any tips :)

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It's normal that there is some latency and it's unusual each time - Internet speeds differs a lot in each country, so, don't worry.
And about this error "Ad inventory unavailable" is okay too, in my apps there are lots of them, it's not a bug - just iAd isn't very gainful. I think and use it like a bonus for free version of paid application.