Here I will reveal the secret behind channels and why they really excist.
Your channel will help you discover what part of your site earns you your revenue, what page, what banner type.. etc Take notice of this.
Adsense sorts adverts in order of Bid highest first, to last.
With this in mind say for instance you have the following statistics:
Header channel = 1,000 views - 1 clicks - $1 - $1
Footer channel = 1,000 views - 2 clicks - $0.50 - $1
Now do you notice the pattern when looking closely at your channels, your header ( the first da block js ) pays out alot more than your footer ( the last ad block js ) because the highest bidding ads are on the header block.
What does this mean? remove the footer and reep more from the header?
Well you could do that, but it's not wise, your footer still makes you a good bit of money.
Each advertisement ad in a block is ordered by its highest bidding ad left to right... this means that id a adblock showing 4 ads is positioned at the top and say for argument sake the highest bidding was 1$ a click and the minimum was 0.5$ a click you have a range. Your footer adblock becomes even less value again 0.5$ to maybe 0.03$.
My suggestion is take a look at your design and click quantity on your channels, if your footer is giving you a really high CTR then its wise to turn your header into 1-2 ads per block than it is 4.
I hope you found this guide useful. check your channels you'll actualy find what i'm saying here is very realistic.