 One very general option is the following. Even though we subscribe to some unrestricted comprehension principle for impossible worlds, we may admit that worlds where only the intensional operators, e.g., the box and diamond of necessity and possibility, behave in a non-standard fashion are less deviant than worlds where also the extensional operators, like classical conjunction and disjunction, do. Let us call worlds of the former kind intensionally impossible and worlds of the latter kind extensionally impossible. This picture (inspired by Priest 2005, Chapter 1) has some intuitive force to recommend it. Kripkean non-normal worlds, where only the behaviour of the modal operators is non-standard (see  section 5.1),  are intuitively less deviant than open worlds, where all formulas may behave arbitrarily. Generalizing, the view would entail arranging the respective spheres in such a way that any intensionally impossible world is closer to @ than any extensionally impossible one.