I found that two ad blocks of 120/600 + 160/600 (one after the other) at the left sidebar, with the

Comment posted to Doubled My AdSense CTR! by Ziv

I found that two ad blocks of 120/600 + 160/600 (one after the other) at the left sidebar, with the inner-up post ad block of 250/250 are the best performers.
It is not only about the CTR – you should look to the CPC.
Though the 338/250 CTR has high CTR, its CPC is very low as compared to those on the left.
So, my CTR is not skyrocketing but my the CPC is very very high – So, I my eCPM is over 5.