With don’t you model the canopy as a “plenum zone” of 5cm width? If you do that you will have access to the surface temperatures of the canopy. In the case of doing that you would have to process the properties of your canopy material to make it work as with 2 layers though.
If it helps you I used the plenum zone as a surface heater on a public terrace to analyse the impact of their surface temperature on the people using it to basically understand how many, how big and how frequent we should have them. The results were looking quite reliable.
The problem that I see is that the temperature under the canopy should not be the same as outdoors, but if you like it better that way it is perfectly fine.