and rightly so, all other things being equal you want all the air thats available, that will definately give best peak power and is capable of giving best power in any situation (forced induction excluded).
If holding the airflow back increases power (and I agree it can do) then something is amiss and you'd find even more power if you sorted that out instead. Fitting an air box lid to increase power (whether it works or not) is treating the symptom, not the cause.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread