From the FAQ:
2.17. I have a video in my post, but when I post to Facebook it’s posted as image preview and it’s not playable.

Support FAQ

This is exactly my problem, but unfortunately I don’t understand how to fix the problem from the details given.

Could someone please break down the steps required to getting a better looking youtube/post autopost.
I also have the youtube address in a separate wp custom field if that helps?

Thanks.