theme twentythirteen does not seem to decrease images proportionately for mobile

I have discovered a few problems with the mobile view of things using twentythirteen. This latest issue has to do with images. Most of my images are not really shrinking proportionately– when I use the mobile view of things. I looked and it didn’t seem to matter if the images were pngs or gifs– they behaved (or not) inconsistently.

If you look at the about page about page on a mobile device you will see a number of images, most of which are pngs, that have reduced to differing amounts.

The trainer picture in the third paragraph doesn’t seem to have reduced much at all- fills up pretty much the width of the screen. Nor has she reduced as much as I would have expected in the next picture.

And in the table at the bottom of the page, the little boxer didn’t reduce much while the logos reduced dramatically- especially when you hold the phone the “normal” way.

I just made the little dog smaller and the logos on the right increased somewhat in size, but I wouldn’t say things were working proportionally. The little dog is now 120px wide (he was 170 and the logos were infinitesimal) while some of the logos are 200px and they are still coming up a much much smaller than the dog.

Is there a solution to this. Not sure what logic is working behind the shrinkage to do what is happening.

Can I or should I change the picture codes to be percentages of the screen rather than use the exact measurements that WP provides on upload?

What I’d ideally like is for the images to shrink somewhat proportionately to their size and the width of the mobile screen.
Is this doable?