It is... but by how much? IS that difference significant? A degree... two... when one molecule away?And I am saying that even the air immediately adjacent to the insulation must be lower than the insulation temperature for any heat transfer to take place across the interface.
The closest significantly lower temperature air may be on the outside of the conduit containing the referenced conductor. The air inside the conduit is much closer to the temperature of the conductor.
No matter what, it still amounts to the conductor operating temperature that is of issue here... not the ambient air temperature.