I have been experimenting with the 336x280, 300x250, and 250x250 formats. My best results came from a "depopulated" 300x250 - 2 ads showing. My theory is that the added white space around the ads results in the highest CTR (not to mention the higher paying ads). I think that Google discovered this, and that is why they are doing the "ad depopulation" thing. So I switched back to the 300x250, thinking that I am set. Nope. Back to 4 ads again. Rock solid 4 ads. Rock solid poor CTR. Less white space than the 336x280, and far less than the 250x250. So how do I reset to the "2 ads in a 300x250" format. The Google experiment works. But how do I get them to do it again, and KEEP IT that way? I'll probably go back to the 250x250, which provides the most white space that I CAN CONTROL. Too bad the font is a little too big.
Google shows the number of ads that its algorithm believes will generate the highest eCPM (per page). That sometimes translates to 2, sometimes to 3 or 4. You cannot control this. Control is an illusion.
Have you tried simulating that format? Place two half-banners inside a bordered box with lots of padding. Turn the borders off on the ads themselves. Yes, you'll see two "Ads by Google" lines within, but the effect will still be two ads.
i do not think you can test this there is lot of know how but basic its down to how much traffic you have. Some one is going to click on your links if you have 100 000 people a day comming to your website.
Surf Dude (cool name btw) I've tested quite a bit and decided to go with a borderless 250 X 250 ad block which shows 3 ads max. on some pages. Lots of white-space and a decent ctr compared to other blocks. For me, that format seems to work best on 'newsy' content (within the content itself) like individual blog posts or short news articles, FYI. K