the std gts-t timing map in a power fc is a timing timebomb.
way too much ignition advance, and the further down the load cells you go the worse it gets, as putting more boost in it makes it access the load cells further down in the map. Do a run with the map tracer on each boost setting and you will see what i mean.
dont kid yourself...just because the afr's are ok does not mean its a safe tune...afr's are only half the battle.
as a quick test go into the ignition/injector correction screen and pull 5 deg out of it (very simple to do) put it on 18psi and see what happens...ill bet its ok as far as knock goes. Caution though as this correction only lasts while the ignition remains on, when car is off this value goes back to 0.
can you copy up the afm settings...i.e. voltage and percentages...ive got a feeling i know who 'tuned' this one.