Change Featured Image Size So Content Title is "Above the Fold"

Hi-

I’m trying to figure out how to manage the featured image size so that the full post title is always visible above the fold when you click on a post. I’ve troubleshot a bit and figured out the the size of the featured image (and subsequently how much content does/doesn’t show up when you first land on the post page) depends on the sidebars. I only want the primary side bar (which I currently have), so I’m assuming (dangerous, I know) that I need to manipulate the featured image files in my child theme.

You can see examples on my site https://www.byjeteast.com –> fair warning; I’m just building it now and there are a lot of bugs floating around, most noticeably weird things happening with post titles. If you want to help with that issue, it’s over here

Please help! Thank you so much. I’m just starting here and this is such a wonderful community of sharing ??