On a T5 raising base boost does not raise overall boost like it did with the old APC c900 and 9000 cars. All it does is ( if you go too far) is to create a boost overshoot into the fuel cut which then creates a thing called negative adaptation ( whatever that means really?) and this lowers your boost. The T5 will adapt itself within reason to any base boost but works best with the one recommended by the chip supplier (only Abbott recomend a higher base boost). I recently heard though that it's not the actual pressure as measured which is important but the actual length of the preload you adjust the actuator arm to. This is approx 3.5 turns from the position that the hole just slides over the pin. If you restrict this working travel in any way the ECU will have more on it's hands trying to control boost.