Really the names are subjective, since both people are really working on the same things but from different perspectives/roles.
The "roles" are in reality arbitrary distinctions for pedagogical purposes
. So, I would qualify that with ..."working on the same things and working ON themselves".... For the arbitrary "role-play" distinction to hold in learning mode, it boils down to individual skill levels and abilities, and whether the more advanced practitioner is willing to help the other and to what extent. Especially considering that the better you get, the "heavier" you tend to "feel" to the other person.