LucidSW - 1:34 pm on Sep 8, 2011 (gmt 0)
CPCs will depend on your QS as well as the QS and bid of the ad below you. As all these variables are very dynamic, you can't make assumptions based on your CTRs. You certainly cannot say that since one ad has a 65% higher rate that your CPC will be 65% lower.
FYI, the basic formula is:
CPC = QS(b) * bid(b) / QS(a)
where QS(b) is QS of ad below you, bid(b) is their bid and QS(a) is your own QS.
You don't say how many clicks for each ad but let's assume you have enough that it is statistically significant. I'm sure your higher CTR ad is a few positions higher which right there means you have different competitors below you most of the time, each with different bids and QS than the other ad.
Also, the first position gets a "discount" for being there. If your second ad is at or near the top position, lower the bid to get a position or two lower. Chances are your CPC will be $0.30 as well.