Sounds like he's doing what he's supposed to (not blowing too many leads), and SIM is doing what it's supposed to (bringing your closer in when they should and not leaving Caldwell in to finish too many games). Do you have him mainly on a 15/20 pitch count or 15/15? You probably also have him on a hair trigger pull count. Bet he has a ton of holds, and I'll bet your closer(s) has a lot of saves. Are you using him as Setup A?