OK, so had a few days free over the holidays to look at adding responsive ads to our older pages designed for 800 width pages.

Adsense home page kept giving us only 3 out of 5 blots for multi-screen compatibility. I have one long page which didn't need a whole lot of changes to make it mobile friendly as it was mostly text in a table, except that it has a 728 wide G-ad midway down the large table of text on the page for desktop use which was of course making the majority of the page 728 plus pixels and thus non-mobile iphone compliant by GAds standards of 320 width.

Swapped it out for a responsive ad, but was not quite right. Then broke the page into two tables one above and one below width-sized 90%, and the responsive ad in the middle of them in its own table (also tried a div with same results). Still not quite right. Ran it through an emulator and it appears that the Adsense responsive ad is not 300 x 250 as I would expect, but rather 353! Then for some reason it allows the bottom table (not the top one though) to extend out to this same width as if it is the new page width!

Adsense Pagespeed Insights ranks this as a too wide penalty and everything in the bottom table starts to come up as 'falling outside the viewport'. Works the same when reducing Chrome or Firefox. Under MSIE 8.0 it causes the page to stop loading at that point altogether in any width!

Sound familiar to anyone? A search hasn't produced anyone else reporting this.

[edited by: martinibuster at 3:05 am (utc) on Jan 2, 2015]
[edit reason] Added paragraph breaks for ease of reading. [/edit]