The OEM detection is actually quite accurate - I personally haven't seen any evidence to say that it erroneously detects engine noise as knock. When the ECU detects knock it pulls timing and the knock goes away, if there were issues with engine noise this simply wouldn't be the case. The knock detection zone can be extended up to 4400rpm, it is more a matter of tuning the system to behave how you want it. Nissan tuned it rather conservatively from the factory.