Featured Images

I’m considering switching to the Fluida theme but I’m having some trouble with the featured images. I have been playing around with customizing the settings, but no matter what I do, featured images are visible for some posts but not for others. Some featured images just don’t show up at the top of the post/page regardless of the settings. Also, some of the featured images fit well at the top of the posts, while others are cropped poorly. This happens whether I select “cropped” or “responsive”. What is the best way to adjust the settings in “customize” to facilitate featured images? Basically, I just want a featured image for each individual post and page and ideally I would like to be able to crop them manually if they don’t fit. Any ideas?

My site is https://www.trailsunblazed.com and I’m currently using the Adirondack theme.