Constraining feature image to use Retina images

Hi,
I have a photo a day blog and am trying to figure out how to use Retina images.
Here’s the site:
http://www.willyurman.com

I’ve tried the plugin Retina WP 2X.

My site uses either horizontal or square images.

For horizontal images, I’m able to double the max width for the page, and the plugin works fine creating a Retina image.

For square photos, I can’t figure out how to constrain the size, but allow double the resolution. If I upload a higher resolution file, it ends up running at the maximum width of the page, which for a square image is too deep.

So I think, if I could constrain the height of the feature images across the board, it would work.

But I’m not sure how to do that. (I’m a lame coder)

thanks for any suggestions or help.

-will