Get some big injectors and a variable FPR from Roland... that'll soon solve any leaning out
I think rolands right a wide band AF sesor while testing on a RR or the open road will probably give you some interesting results. Can't see the flap on the airbox being an issue...if anything I'd say it being fitted and reducing flow then suddenly opening it to flow would be more likely to cause an issue than it being open all the time??!