I noticed on Element (Matrix/Gitter) that the preview images for links to doc and dev were pretty random, so i added socialnetworks_twitter_site_name, socialnetworks_twitter_site_image , socialnetworks_facebook_site_name and socialnetworks_facebook_site_image for them both.

I guess themes etc will need them too - also, they're in a really bad place now (the legacy tab of the social control panel, i'll add them the metatags panel too, which is where i thought they were...)