[mwebb]

..."I admit an increase to compression likely doesn't happen to all cars. ."... ..."" I could see how an increase in compression is possible."...

what ever you may think
(excepting the effects of EGR and variable cam timing)
the engine compression will not change on any car except some SAAB engines
which have variable compression due to a hinge strategically placed in the engine block

the words you seek are
peak Combustion pressure
but do not forget IGN timing will change based on MAP changes and
it is possible that the authors of the article you read were experiencing some of that

..."
A cleaned up air intake can only make a difference when the throttle plate is wide open, "...
i agree with this
but i believe the OP's intent was to fabricate something to pressurize the intake
like RAM AIR on an old Pontiac ...

however i may be INcorrect --
if the OP was referring to the brightly colored garbage with conical filters that ingest hot air from under the hood sold by the alleged "performance outlets".