The size of the ad container needs to be spelled out in your css and your css needs to be accessible to robots. Google uses your viewport settings and your css to determine what ad size to deliver. I have seen them send the wrong size until they get all their signals together.

My worries though, is inadvertently violating Google's guidelines. If they load in the wrong size, am I not technically obscuring part of the ad or content (in case of an overflow)?

I gave up on responsive and put a bunch of square ads in. They work well on both mobile and desktop.

At the top of my pages I was using a responsive 320 x 50 but that wasn't getting many clicks therefore changed it to a 320 x 100 and that is getting clicks, 5x as many.

At the bottom of pages I use a responsive 300 x 250 and that gets a good ctr, in excess of 3%.

Insofar as I am aware I have not had any problem with them displaying and I certainly have not specified any "extra" coding other than the copy/paste.

I gave up on responsive and put a bunch of square ads in. They work well on both mobile and desktop.

For the ads in my best-performing placements, I have too. I still use them in some spaces, but I've found that CPC rates for standard 300x250 unites -- which Google recommends for both mobile and desktop -- are about double what responsive ads were performing on my site.

I don't think this will be the case forever -- I believe more and more advertisers will gradually create more ads for mobile -- but it's not going to happen overnight, and that's likely why we're seeing lower CPCs for mobile.

Plus, and netmeg has posted several times about this, the user experience is different on mobile -- users are doing different things. So you really need to think about that when you place ads and design pages. Event sites can do well, and locally-targeted can do well too.

For the ads in my best-performing placements, I have too. I still use them in some spaces, but I've found that CPC rates for standard 300x250 unites -- which Google recommends for both mobile and desktop -- are about double what responsive ads were performing on my site.

Have you tried the 336x280 size? That's what i'm using right now. So far things are looking up. Revenue has definitely improved since i switched to this ad format. I used to have a leaderboard ad on top, a 300x250 midway through content (I have really long single page articles), and a leaderboard at the bottom. The in-content ad used to be my highest performer. Now the top ad is best performer. I'm curious if there is any real difference between 336x280 and 300x250.

Have you tried the 336x280 size?

Actually I have and while I wasn't necessarily disappointed, 300x250 have performed better for me. I'm always open to try them again -- AdSense sent me an email this week suggesting I give 336x280 another go -- so perhaps I will.

The consideration I have to keep in mind is that my audience is majority mobile on the weekends by a large margin, and so I need to show ads that can fit within most people's mobile phone displays.

Phones are becoming larger, however, and I think a year from now 336x280's will likely work just fine for mobile -- especially as more people upgrade to the iPhone 6 and 6 Plus. But for now, the 5 series iPhones are still the majority, and so I need to serve ads that won't break the page in those displays, so that's why I stick with the 300x250.

Don't you have to muck around with the viewport size to display 336x280 ads properly?