I think this post sheds some more light on the issue:
Inside AdSense: Another look at optimizations
Although it is still a bit vague... but what else would you expect from Google?
Will.Spencer (6 April, 2009)
I have a question about this, do you think it's ok if I place my ads like this:
Thanks for your help!
@ Dusan - That placement is okay.
Need some time to handle deferred joining date by three big IT companies.
If your work is still pending, I'll soon get in touch.