MK5RS2K

my car is running 270hp at the moment on omex 600 management.it was mapped with a afr of 10.7 on 1.2 bar of boost with 97 ron.my exhaust was causing me problems due to it being 2 1/4" so the tuner didnt want to make any mre power due to it being close to det.i now hav a 3" straight through exhaust,what afr's should i aim for? cheers