I had my Leon mapped at R-Tech, fantastic service and quality (CR Turbos hybrid K03 fitted)
Now upon my first session with Niki, the car made 265bhp at 1.3/4 bar, and feedback then is it wouldn't flow. I too was also supposedly running an uprated downpipe with sports cat, but clearly there was an issue (supplied and fitted by Blueflame many years ago).
I decided to pull off the downpipe and sports cat to take a look....
downpipe was barely measuring in at 2.25" (awful restriction) and the sports cat (200 cell) was also restrictive.
I replaced these parts with a decat and 3" downpipe (I also fitted a supersize TIP at this point). Car went back to R-Tech and made 291bhp. Flow is key and just because a well respected exhaust manufacturer state the exhaust is of good quality, doesn't mean it is.
If a car won't flow and Niki is reporting it won't flow, then somewhere on the car the hardware isn't up to scratch.