Mike L. right with Type Manager being Org or Site level. It's all about Policy Administration at context level. Don't grant anything even team member role. You will have to remove the standard OOTB access to WTDocuments which is top level. For the context with subtype on, just add access to only the subtype and not top Document Master. For disabling the subtype, put a deny on the subtype but allow create Document Master.
In Reply to Brian Wilson: