Contstrain height of feature image

Hi,
My site uses a Featured image on each post. When the image is horizontal, Retina 2X works fine.
But with square images, if I upload an image at twice the resolution it displays twice as large.
I assume (though I’m a newbie at this stuff) that the width is constrained, so it loads the higher res 2X version.

Is there a way to constrain the height so it does the same thing?

site is here: https://www.willyurman.com

thanks!
will

https://www.ads-software.com/plugins/wp-retina-2x/