@alxmedia
Thank you for your answer. Unfortunately, your suggestion didn’t work. I’m not exactly sure why, but the dimensions were completely unaffected by any change I made (even though web developer tools let me see that some change in code actually occured).
However, your suggestion did actually help me solve the issue. While looking for the line you mentioned, I found the line:
add_image_size( 'minimer-list', 320, 320, true );
So I modified the content-featured.php file to load this line instead of the one you mentioned. This did the trick!
Thanks a lot for your help and amazing themes. The theme I’m working on is a mix of Minimer with Enspire, a little bit of Readline, and some of my own ideas.