Although the vent on the Evo is clearly for the engine, wouldn't it help suck air through the FMIC too, Glass?

 

Here is what I make of it

1. Coolant temp + under hood temps = interelated

2. The more airflow you can get the more cooling capacity you have (as more molecules of air go through the radiator, ic, around engine tec. etc.)

3. You can only get x amount of air in/out with a certain configuration (Mazda redesigned the front lip on the 99+ to redirect air around the radiator duct as the flow was so large that the incoming air could not actually enter the duct at certain speeds!)

4. Hot trapped air (heat soak) has an exponential effect on underhood temps

Conclusion

A vented hood increases the amount of air that can go through the engine bay and hence decreases engine temps