I've never got to the bottom of why, I have done enough research in the software to eliminate any limiting by the DSG software, and it doesn't seem to be an engine ECU software issue either. Most manuals use an EDC17CP14 ECU and DSG use an EDC17C46 ECU, the method of tuning is the same but we never get quite the same gains from the C46 ECU. It's not just us either, Revo seem to get the same outcome.