Well, not exactly sure where to check temp in my exact case, but nowhere lower on the cat, or exiting the cat to the exhaust flange is the temprature higher than at the collector. It's the same or cooler. But that doesn't surprise me given the configuration. The collector and entry point is in front of the engine behind the radiator. The bottom/exit is probably in the air sufficiently to get cooling to the atmosphere and isn't directly mated to as much thermal mass. So it' either toast, or that test is not so relevant in the case of the Aveo.
NOTE: cat comes straight off the exhaust manifold is what I'm getting at. It's not located under the car.