Placement of large rectangle ads

I've recetly experimented with ad placement. The rectangle ad atop my page here, was recently on RIGHT side of page....the location where almost everyone said you ought to have it. Well, I won't say what my CTR was or is now....but when I moved that same ad over to LEFT, my CTR increased by over 100%.
So my next question is, how do they know that the large rectangle is the most popular? I mean, is that the ad format that performs the best or could it be the 720 wide banner atop the page? Some things make you wonder.....

 

That is why you need to test what works for you.
Run 50:50 split tests and constantly try to optimize your ad inventory.

 

A good advice for me but how can we ad rectangle in the post like you did at blogger?

 

I think they know it is the most popular because adsense said so and they have the best stats about that
But it could be different for different sites/ad placement. But the big square ads are so big, it's normal it's the best performing. If they provided a 640x480 ad, I bet it would become the best performing one

 

Interesting, mine are currently central so I think I should probably try testing them on both the left and right sides even though it may look a little awkward!