No problem Spit, feel free to "barge in" whenever.
The inlet lip I am using was made yeserday from styro foam. It is just a rounded inlet lip, 6mm wide that goes around the inlet of the fan. This smooths out and transitions air from around the immediate area in front of the fan for easy "ingestion". In a ducted installation like yours *generally* an inlet lip is not necessary. If there is a step in diameter (enlarging) of the ducting right before the fan or if the ducting is bigger than the ID of the fan housing, you'd want to make some sort of "ramp" or inlet to smooth the airflow heading in. Ideally, the design of the ducting you would like to have would be like Klaus describes here
I don't have an Alfa plane to measure or critique, but I have heard there is gaps around the fan unit that could allow air to flow past (or blown forward) of the fan. This is not conducive to maximum performance (unless it was intentionally designed to couteract some other design problem). By taking the time to make a proper sized outlet ducting (and inlet). performance can be upgraded for "free" in that no more watts are needed to reap this lost power. Remember, turbulant air is harder to convert to propulsion and conversely can decrease air velocity (efflux) if it does not have a continually smooth duct to escape through once past the fan.