Turns out that not only do I have to add <p> tags to the template, but if my posts are too short, FB doesn't infer them as the description for open graph.  Not only that, but I can't set og:description myself because I don't know how to get at the post content from the html header.  Soooo as a hack, I'm just inserting lines at the bottom of my posts.  Yay. -_-