Post Type Grid Image Sizing Results in GTMetrix “Serve Scaled Images”

When I run a page speed test using GTMetrix, I get a 0 Fail for not serving scaled images. I traced it down to the image resizing done by the Post Type Grid widget. I like how this widget looks for my site, but I don’t like that it gives me this error.

In a thread for a different plugin that had the same problem, it appears that’s something they can fix, possibly related to the fact that the height alone is adjusted via CSS. Is there a way to address this?

I do like this plugin, but I also want to address slow page load problems.

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