Miami Defense is missing a lot of player's this week and they have a lot of other probable players out there. Basically, you're looking at an extremely banged up unit out there at the CB and DT positions, which should lead to decent games from all the Cincinnati Johnsons.
Personally, I think Johnson is a never bench player and that Mason should only be used over CJ in the most extremely favorable matchup. Indy's secondary looks pretty weak but I would not be comfortable sitting Chad to start Mason against them.
Basically your choice is between Mason and Foster in the slot. If you saw the last Sunday Night Den vs. KC game, I think it's pretty safe to say who is the better option.