It might be word count to ad count ratio. But most of my articles on third party sites that lost rank were in the 800-2000 word range, most over 1100 words. And not "wordy" - as in, they wouldn't have been identified as blah-blah-blah-beat-around-the-bush-to-say-nothing text even by an algorithm. They're clearly organized, too, not just meandering paragraphs.
Not saying this to defend my articles - I've been a writer since I was a kid, so whatever I write I always think is brilliant, then crap. :) Just trying to figure out if it's something simple, and I don't think so. The magic bullet isn't obvious.