How to turn off Featured Image Header

I’m trying to figure out how to disable the Featured Image Header feature of this theme. I love the theme it’s self but it seems like the theme is randomly using some of my featured images to replace the site header. While I can understand how some people would want this feature, I don’t need it. I can’t seem to figure out what is causing the theme to switch the headers on some posts (but not others??)

Any ideas on how to control that option?

The header should look like the header on the front page here:
https://alley33.com/

On a random post where it’s automatically switching out the header for the featured image:
https://alley33.com/down-with-pants-a-qa-with-designer-alyson-clair/

On a random post where it’s NOT switching the header:
https://alley33.com/designers-qa-with-alley-33s-own-amelia-2/