Not Using Proper Thumbnail File

I’ve specified on the plugin that we want to use a thumbnail file for our top posts which you can see in the screenshot below:

https://www.evernote.com/l/ADXFA3VxXatAUZhaZwME0Ro4Ytttxh_1f2c

However the image being used in the top 10 posts list is the original file resized to the thumbail size. How do I get it to use the actual thumbnail file? I’ve confirmed it exists and can’t find any reason why it wouldn’t be used.