The baro will only function at its set limit. In other words, if it is set at .05, it will begin to open to keep the draft from rising above that. Below its setpoint it will remain closed. It will not increase, decrease or affect your draft other than making the setpoint the most draft it can have, a limiter if you will. If you want to reduce the .04 draft lower, take the weight knob off and try a nut and washers until you get the weight you need for the draft you want. Be sure to confirm your draft readings. If your lucky, that weight can be slide to near the far end to reset the baro for high fire at .04. Don't shorten the chimney.