The og:image tag on your page is using an image that's too small. If your og:image tag is under (I think) 1200x600px. To get the larger image posts, you should use a larger image for your og:image tags. JFBConnect will try to get the best image, but if the image on your page is too small, JFBConnect can't automatically make it larger.
A tool we recommend is
Social Debug
, which can help you more easily see your Open Graph and other social meta tags, as well as show you want your post will look like based on those tags. If you set a larger image, you should see an improvement in the example posts there as well.
That tool will also automatically refresh Facebook's Open Graph cache for your page so that your changes will take effect immediately for existing and future shares.
I hope that helps, but if you have any other questions, let me know.
Thanks,
Alex