This is why Things are dropping:
1. New ads have been rolled out. They look stupid like headlines. No idea why G implemented them.
2. September and October are bad months. Really, whats happening? Late october/November there should be lots of New advertisers and great deals (but what will that help if visitors just see a headline? :) )
3. You get lots of inrelevant ads. Just check and you will see this is really irritating and might be the nr 1 reason why CRT has droped.
There are ways you can try to solve this.
You can get normal ads back. They just show headline, 2 text lines and link. No Arrows, no fav icon. (god i miss these ads)Just turn off the enanced text ads.
I have tried this and it seems like CPC is dropping.
In adwords advertisers have been moved over to enanced ads. If Your site do not offer this then you might not get all advertisers or G punish you some other way.
For me it feels like just staying With enanced design and just hope G brings back the old ad types With fav icon and Arrows. Don't know why they changed it, perhaps they where just too good?
Sorry for bad English