Website visitors are mostly clicking on the website top area. That is why I mentioned about the fact in earlier post as well. Very mostly your website header or the site Navigation(website main links) are going in the top area of the web page (coloured in red). You have to be very clever and careful about the add setting there with Navigation and the site Header or what ever you are going to place in header area.
Most Suitable Add Placements In The Header Area
1. With in the Header and Site Navigation.
2. Top in the Header
3. After the Site Navigation.
My best choice is 1st One.