You can invoke aspects at the time you create potions to increase their effect. In the case of hanky vs. ghost dust, I assume it is because of a change in Harry's Lore between SF and GP.
A potion like the Scent Suppression, I would always set a base duration of "one scene", because that is how long it needs to work anyway. For combat potions, I would set the duration as per evocation rules, 1 shift per exchange, but this is something to avoid a conflict, and having to reapply something like this every few moments is kind of tedious.
