Self-links are sometimes sent as comments other as mentions

I have the plugin installed. When I publish a post A in which I link to a previous post B in the same blog, sometimes a mention is sent, but others a comment (always through the webmention protocol). Though there is no clear pattern, it seems to depend mostly on whether post A contains an image. Could that be? Or am I missing something more obvious? And can it be controlled somehow? I’d like all links to be self-notified as mentions, as I don’t feel like linking is “commenting” on anything. Thanks a lot.