Theory or experience matching content type and AdSense type/placement

For example: On forums I've seem AdSense at the top and at the bottom

[Webwork]

I accept that placement and ad format is a "plug and play" process: Plug it in, see how it works and adjust. What I'm asking what has contributed to your placement theories: What is your theory/data in support of where you locate AdSense ads and what type of AdSense layout you choose?

For example, I've seen AdSense at the top of thread in a forum and I've also seen AdSense at the bottom of forum threads.

Forum Theory 1: At the top they are most conspicuous.

Forum Theory 2: At the bottom they may equate with "and here's more information about what you just read in the threads..."

Forum Theory 3:?

Pure content page Theory1: Sideboards don't interfere with the reading process and yet are still visible.

Pure content Theory2: Leaderboard because? Footer AdSense because it's "more reading"?

Pure content Theory3: New "big box" AdSense mid-article...because?

What is your theory or proof, by content type or content format/layout, for what works or doesn't when choosing where to place AdSense and what AdSense format to choose?

[Roomy]

I run a pure content sailing site amongst others and have found that wide skyscrappers in the left hand margin seem to work best. Sometimes the ad content is a good match and sometimes it's just generic sailing ads, like "learn to sail here" So I figure best to keep it well away fromt the content. I figure the psychology runs something like...

The content gets read, then the visitor scratches their head thinks, "ok now what?", they see an ad and think, "hmmm I'm into sailing and that looks interesting even if it's not exactly what I was looking for",...click.

The above is based on what I do! any similar thoughts?

I am experimenting with a large panel at the top of the content on a really popular page and it looks to be even more successful.

[yump]

In the absense of any solid published research, perhaps the best bet is to go by your own reactions to ads on other sites and also by any reactions from any friends, colleagues, acquaintances etc. to different placements.

We've also made a list of reasons why our visitors have probably come to each page running adsense, are they after a quick result for something or are they likely to be reading carefully. Are they browsing around or are they likely to very directed....and then asked - why would they click on an advert on that page when they are in that particular mode of looking?