I can see already a way to do this is setting the root from FATAL-DEBUG and restricting access by appender
You will need to do just that. Like Luis said, it’s a funnel. LogBox decides if there is a matching category to handle your logging and if not, defaults to the root one. The filters on the category are applied and whatever is left now gets sent to the appender. At that point, the appender gets to decide what it feels like logging based on it’s min/max, but the category still gets first say.
Obviously then, it wouldn’t make any sense to assign an appender to a category in which the appender’s min/max were more liberal than the category. Unless, of course, you were sharing the appender between multiple categories.