If you have too much overhang, it will start to move huge amounts of air between the inner and outer tube.
A guy in Germany does a lot of testing and makes YT videos about it.
So he tried to measure the airflow in a double wall tube: with a 10mm overhang at the back, there was just over 40 km/h airflow between the tubes. With an overhang of 20mm, this jumped to over 110 km/h (this is quite a lot of air being moved).
It won't get hot though, not at that short distance. The inner hot flow will not mix with the outer flow enough in that distance.