Featured Image Size

Hi guys, not sure why I never received a response here… normally you are spot on and fast to reply. I am just curious if there is a way I can edit the thumbnail size so it matches the aspect ratio of the feature image in the blog post. It is frustrating that they pull from the same image but one is a square and one is a rectangle.

Is there a way to modify so that the featured thumbnail is a rectangle, or the blog post can just be a square?

Thanks in advance,
Matt