Cannot enable Summary Large Image Card?

Hi,

I cannot seem to enable Summary Large Image card in your plugin. I see in the changelog that it was implemented a few versions back, but I can’t seem to find the option for it when publishing the post. I’ve attached the screenshot here:

http://www.evernote.com/shard/s53/sh/88ce281a-d0b0-41c6-95de-8f3dd2948faa/c4f15c62189e8a0296fa2d74bad636c2

I am only getting the Summary card on Twitter. You can try the following link yourself to see it in action:

http://thirdworldstrategy.com/leverage-social-media-pakistan/

Am I missing something? Please guide me how to get it working. Thanks!

http://wordpress.org/extend/plugins/jm-twitter-cards/