this is a guide i once received - and it confirms what you're saying

To increase both the peak and held boost pressure figure, increase the bleed size of the amal valve port labeled “R". (Viewing from the top it’s the right hand one)

To increase only the peak boost pressure figure, decrease the bleed size of the amal valve port labeled "C".(Viewing from the top it’s the middle one)

As a last resort only:
To Increase both boost pressure figures, decrease the size of the amal valve port labeled "W" (Viewing from the top it’s the left hand one) decrease the bleed size of the amal valve port labeled "C".(Viewing from the top it’s the middle one)