The inlet is a strange thing to analyze -
It appears to be a "ram air " inlet - it isn't.
actually -the air behind the prop - at the base of the prop -is somewhat stagnant (?)
What I mean is that it is swirling and moving outward at that point on the prop--so no air is being rammed into the cowl.
The exit air (lowering of pressure in the cowl) is the controlling factor.
a very small inlet does the job as long as the exit air pressure drop is sufficient

you can theorize about this ----but in real world application - -you have to cut n try
the why is because the engine heat will vary -(obviously ) as power output increases
Higher speed will produce more effective low pressure so that can appear to be a self controlling (closed loop setup) - but it ain't.
You have to sneak up on the setup.
the why is that the power -while increasing -tries to increase engine temp - which is not wanted -- so--you have to have the setup matched for the wortst case (most power) scenario.
On the big twin --lots of guys got this wrong -they figured air rammed into the cowl - which is not so -
Here is another pic of that setup which has a very small inlet and a HUGE low pressure setup. on a .50 glow enginbe --this is all far easier as alky fuels cool much better than gasoline fuels. ( fuel to air ratio) The large bowl shaped cowl has as it's exit a semi circle with a lip on the LE to cause lowered pressure. The engine ran very cool under all conditions