You can use a similar mechanic for types of enemies, in order to get a varied but area-appropriate mix:

(goblin) 5, (goblin soldier) 2, (wolf) 1, (hobgoblin) 1

Over the whole area, you should get 5/9 goblins, but any given room can be an interesting mix -- 3 hobgoblins and one soldier, 2 wolves and 2 goblins, one of each, etc.