The blog I have with the most traffic is not making money...yet one of my blogs that gets very little traffic just got a big click. I would think that the high traffic domain would be converting but it's just not....so frustrating!
click price has nothing to do with how big your site is, it is much more specific to the keyword of the click and still is sometimes a matter of luck sometimes a small site will get a higher ctr because a larger site the people are busy reading the site than clicking on ads
by high traffic i guess you mean entertainment niches ???YES !! they always convert poorly and is the cause of SMART PRICING for several people all around the globe so avoid them
Test your adsense position and formating. If you are getting a lot of traffic, you really should focus on your conversions