Looked at the two tags. Did a search for covering -solo -covering_self. Got a single page of posts, of which maybe FOUR of them actually classify as not covering self.
Did similar check of covering-self -solo and two images that I saw weren't self-covering (and were retagged) were being covered by another person.
By default, any picture of covering solo counts as covering_self; any case of covering_self also counts as covering.
Thus, I propose that covering_self alias (not imply) to covering for ease of use and similarity.
Updated by Riversyde