Featured Image settings

This is going to be a rather rudimentary question and one I should be able to find but alas I’m having issues locating the answer. But in playing around in the settings and in particular using “Display Excerpts on Archive pages” and placing the read more option to show the excerpt in the archives I get the thumbnail image along with the featured image in the archives. Is there a way to pick and chose which one appears?

For example I have around 800 posts and most but not all use a 600 x 400 image and some use a 300 x 450 or so for movie posters. For the majority I would love to display in the archives list the larger image but for posts on movies I’d like to show the thumbnail. So is there a way to move back and forth between the two options?

I hope this question makes sense. Here’s my site: https://www.internationalpolicydigest.org/