I say afk doesn't work because if you have to be there to babysit it your not truly AFK, but yes if you are able to keep it open for 3.5 hours whike sitting nesr it you should be getting 5 levels. If your getting less that's a bit weird but I don't have enough info on that to be of more help I apologize in that regard
Oh true! You’re correct on that. You can still get xp from the lobbies, but it does suck that you have to watch it constantly for the 3.5 ish hour timeframe.