In the design of 3E supposedly percentages are used to donate conditions which cannot be improved, static conditions I guess. That puts fortification in a somewhat different arena than normal stacking rules. I agree with Hypersmurf it feels like it should be check one, and then the other. I know that if someone is blurred and blinking I do both. As far as blurred and displaced I haven't been in that situation, but I could see checking one then the other. Of course total darkness offers a 50% miss chance, so I may have to think about that.