You've always said to me that an S4 MAF is whats used, and what you used on your car mate.
http://www.seatcupra.net/forums/showpost.php?p=3340154&postcount=30
RS4 is a MASSIVE MAF and the calcs dont add up to me.
The only way i can see it working if you max out the 2.5bar MAP sensor so your ECU thinks at 2550mbar your MAF readings are really high but you'd have to run a lot of boost for this.
The ecu expects to see certain airflow at a certain boost and if it doesnt it will add fuel in and your trims will raise to accomodate. This is why you used a 3 bar map sensor, as it drops the read boost pressure by ~500mbar making the MAF reading vs. boost closer to what it should be.
For example:
If on a 2.5bar map maxed out (vag com reading of 2550mbar) you would see say 220g/s max but the ECU expects to see 250g/s at this boost level you would see your LTFT rise to about +15%.
Now on the same boost level but with a 3 bar map (ecu now reads ~500mbar lower but the car delivers the same boost) you would see the same g/s but your fuel trims would drop as the car is seeing more air flow for a reported lower boost.