Featured image sizing in post-mode on Blogs MU theme

Can someone tell me if the featured image needs to be set to a certain size for it to show up correctly on the home page of the Blogs MU theme? I've got my Service Settings set to post-mode, but I have one image in particular that is cut off and showing up blurry, no matter how many times I've resized it. It's weird because the other images are not doing that.