I've just installed an AVCR and left the boost setting a little over 1 bar (14.5 - 15psi) and adjusted the duty to hold the boost through out the RPM range

When I'm giving her full throttle, i noticed my air fuel gradually running lean from almost rich....
is this normal, or am I gonna risk detonation???

mods are:
Air Intake, Catback, Apexi AVC-R

um wow.. of course it will do that espically at partial throttle

thats why people get a reflashes. they have the fuel and timing maps to match the increased boost

not saying an avcr isn't a good product just that the wrx/sti ecu is not set up to deal with the boost in stock form

and hopefully your not using the rear o2 sensor for any kind of valid information