I have a RV-7 in East of France, similar weather as where you are...
My engine is a Aeropsport Power IO-375, with fuel injection and dual P-Mags (electronic ignition). My setup probably helps with lower CHT compared with carburator and "traditional" ignition...
During the first few hours after initial flight in summer I was seing hig CHT as well, but my engine was not broken in and the weather was quite hot (above 30°C). To mitigate the hight temps I was climbing at 120 Kts indicated for better airflow over the cylinders.
Now I have about 50Hrs on the plane and the engine break-in is done, and I'm able to keep CHT below 380 most of the time.
I believe the most important is to have PERFECT baffles.
That will help create a high pressure area in the top part of the engine compartment forcing air around the cylinders for cooling.
If you do not have good baffles this will make leaks over the baffles or on the side of the cowling likely and this will reduce the high pressure on top of the engine and reducing the flow of air around the cylinders.
When I built my baffles I took very good care of blocking every little hole, and making tight rubber seals. As others have said the inlet ramps are also important to allow a smooth airflow to enter the engine compartment.
Increasing the exit area will not help cooling the engine if the baffles are not good, it will only increase drag (your cowl flap will get in the airflow, so more drag).
In summary I believe the key is the pressure diferential between the top and bottom of the cylinders. The higher the differetial the higher the flow of air around the cylinders and thus better cooling.
EDIT: link to a good article on baffles: https://blog.aopa.org/aopa/2017/03/29/its-baffling/