For me, I figure out how the bonues apply by whether or not there is a target that resists the spell. For an attack, someone rolls to dodge so its offensive. For a block against damage, its defensive. For a block against someone else's movement a la Orbius, its offensive, because they resist the effect. For a maneuver on yourself, an ally, or the scene its defensive, for a maneuver on a zone or an enemy, its offensive. For a counterspell, its debatable, but the book describes it as an attack on a spell effect, so it would be offensive.