Can't Play as Custom Leaders

[Mediocrates]

I'm not able to play the full complement of custom leaders in either a modded scenario or custom game. Only about five or six custom leaders appear in the leader select drop-down menu. I've looked over pretty much all relevant XML files (specifically MLF_CIV4ModularLoadingControls) and haven't found anything out of the ordinary. I don't know if this is relevant, but I had this exact same problem with Rise of Mankind: A New Dawn


Also, where do I need to put the extra custom leaderheads?