I'd best leave it to BoB
It looks like it requires uploading a cut-up version of that header image to the server rather than that layered hack in the style which positions the ad bit on top of a whole image - which is how it should have been done in the first place. But I'm too tired to do that right now

Plus I can't see the ads in my browser anyway (doesn't load from pagead2.googlesyndication.com, so I get a blank space - as a result, the style looks perfectly fine to me right now

), so I won't know if what I've done looks right or not.