First let me say, thanks for the great plugin. I'm looking forward to getting it setup correctly on my blog.
Using twitters card validator (https://dev.twitter.com/docs/cards/validation/validator) I was able to get everything working except the post image. Image on the main page is working great. It looks like it's linking to the featured image from the post but I'm guessing because it's 3mb it's not showing it. My theme resized the image and uses a smaller version, is it possible to have JM Twitter Cards grab a smaller version of the featured image?