Whole lot of debate over nothing.
If a fella wants to cover all bases during construction, rather than waiting until after test and break-in to judge temperatures, well, why not?
The Vans mantra is balanced performance, an airplane with a wide operating range that does all things pretty well. A builder can make choices which add to the range (go faster, stall slower, etc), and remain in accord with the mantra if his modification does not subtract from performance elsewhere (for example, go faster, stall faster).
Here the subject is cooling. The ideal approach, when incorporating changes early in the build, is to widen the cooling range at both ends
How? Assume the builder wishes to use something like Nimmo's doors. Determine the additional exit area provided by one
door. Section the stock cowl exit so as to remove fixed exit area equal to that one door. Now install two
The result is one door area less than stock in cold cruise, and one door area more than stock in hot climb. That should be a useful range addition given stock inlets, baffles, etc. Frankly, if it won't cool with one additional door area, yes, there are other issues.
The concept can be applied multiple ways, and with system
mods the cooling range can be extended even further.
RV-8 stock exit. Compare with below. (Yes, the pipes had to be modified):
Don't really need doors. Instead build swappable exit panels for hot and cold seasons:
Very small fixed exit (on right, above), installed for winter:
Even less fixed exit area....
....with low drag variable exit area: