Based on my experiments here, when a comment is crossposted on FB, the original entry's title does not appear anywhere on the FB. See this capture here:

When the comment is lacking a subject line, the first line of the comment is turned into a link. When the comment does contain a subject line, the title is then turned into a link, as seen in this capture:

Also notice in the second capture here (it's a comment from kr8zykat to xwacky's comment), the FB post doesn't mention xwacky's username, only shows the username of the journal where the comment resides.

If you do any testing on a comm, I'd very much like to know the outcome too!