It's generally agreed that text in <H1> will be given more prominence than text in <P> by the AdSense algorithm.
Does anyone know where <H4> <H5> and <H6> live - are these more important than <P>?
And, is <small> also less important than <P>?
As discussed elsewhere, I wish to assist the Googlebot by making sure it knows what's proper content and what shouldn't really be part of the content on an article page - like navigation or copyright statements.
I don't believe the mediabot and/or AdSense algo gives any more weight to what is in <h1> tags than what is in any other tags. It does give importance to what text is closer to the top in your code, as well as what text is closest surrounding the actual AdSense code. The mediabot behaves quite differently to the googlebot, which does weight font sizes and tags differently.
People have had ads targeted to keywords within the navigation, so it doesn't recognize navigational text as being any different than the page's true content (ie. article), even if that text appears in every single page within a site.
Jen would have agreed with you up to the last couple of weeks. Having just gone through a major refresh of the site, media bot seems to pick up on text slightly lower in the body, maybe the second or third paragraph. Strange happenings but no doubt about it here that ads keyed on that section of text and no others. Going to change it again this week and will see if ads follow. Definitley not off of <h1> tags as they are generic.