Well, living in the 50th State, I would take any incoming filtered air that was cooler than the ambient air under the hood in sufficent volume to feed the fuel distributor. Yes, you can measure the difference in temps, just head out to your local Bed, Bath & Beyond and get a couple of probe thermometers, or just one if you don't want simultaneous readings.

I have to admit that I have a K&N cone and tube intake kit on my W201 2.3L. I also know that it's probably drawing warm air from under the hood, despite trying to locate t as close to the headlight/radiator duct. There was no change in MPG after installation, so at least it hasn't cost too much performance. I haven't given up hope of being able to thermo shield the K&N and getting a duct down to the bumper slot level. For the time being, I just enjoy the sound the engine makes.

As for other lower fuel mixture temp "techniques" I will always remember how Penske used to chill the Sunoco fuel drums and even the car's fuel tank in a freezer locker before fueling Mark Donohue's TransAm Camaro.