I came across this paper by Tatiana Shulga: Mediated Presence in Role playing game/Virtual game. It's actually a french paper of sociology and it deals with how presence in mediated in two kind of game: RPG and MMORPG. The author presents interesting concepts (like how the tools used in RPG supports presence) and put them into a relevant sociological framework. She also describes a model made up of three "plans de présence" (presence levels).