On a previous WRX M/Y 95 I had a cone filter breathing under the bonnet. I did quite a few experiments using a Halfords outside/inside thermometer and a gardeners Min/Max thermometer.
I came to the conclusion that the benefits from better breathing were substsntially lost due to temperature issues.
My solution was to make a reverse cone to fit over the air filter and bud it up to the inner wing. This took three attempts to get spot on but then I was able to seal with tank tape to the inner wing. The snorkle was dispensed with. Subsequent experiments showed that the inlet temp was always 2-3 cent over amb. except when stationary.
Now the interesting thing about all this apart from the car being friskier was the mod cost about £3.00 PVC drainage type pipe came from a local fabricator. About 3 feet and by the third try and a couple of jig saw blades later it was a good job. Think it was 9" or 10" dia just cut and cone formed. Up to inner wing air intake / snorkle hole. Also covered the pipe in silver baking foil.

 

I run a panel with the resonator removed and the snorkel hole blanked off for similar reasons. Never did the measurements to back it up though, thanks

Richard