I used to believe first appearing adblock (in code) has always highest CPC ads but recently i focussed on stats and found this is not true for all websites.Most of the websites do go with this myth but some do not hold this myth true. So do you think type of adblock has also some co-relation with cost per click?
Mong, Lets see how "adwords" performs to understand the ad's we get on adsense this kinda explains that better keywords and ad text will get priority so maybe in your case the same thing is happening and the top bidder is getting the second spot.