I'm really not sure how much the hot air from the cat. affects the intake pipe above it, as, although it will get the hot air, it is drawing fresh cold air in directly from the nose of the car, and this will actually cool the pipework so the air going into the engine will not actually be traveling slow enough to get that hot, slightly warmed over, maybe, and obviously not as dense as completely cold air, but I doubt it is measurable from the driving seat. A simple aluminium shield above the cat. would also help, of course.
