Images ratio changes when resizing browser window

Hello,
Congratulations on your Grid Plus plugin.
I found that after adding a grid to a page (https://www.limitededitionprints.co/prints-test/ ), I shows great on the page, with its original images’ ratio, in my case, 3:2. But the moment you resize the browser window, the images are resize and cropped to a new ratio, and therefore modifying the original image ratio.

Is there a way to keep the ratio all the time, even when resizing browser windows?

Thank you very much,

Jordi

The page I need help with: [log in to see the link]