No clues. I just looked at the page, and I see no og:image tag at all. Is the module currently published there, or did you disable it?
Can you try testing with a different template, to see if that makes the og:image tag work as well?
Not really sure why the module wouldn't work. It doesn't matter the position you put it in, as long as it's a position that exists on your home page. The tp=1 query string parameter is disabled on your site, so I can't see what template positions are available to give recommendations. The best I can say is to put the following in the custom HTML module:
TEST {JFBCGraph image=http://site.com/image.jpg} HEREThe output on the page should look like:
That's because JFBConnect will strip the { } tag to create the Open Graph tag and just leave the other text.
Hope that helps you diagnose the issue,
Alex