It alters fuel metering off idle, but the idle speed doesn't change - don't ask me to explain that, though. This is why an "ALDA tweak" makes the car so much more responsive... it's increasing the fuel delivery curve above idle. Maybe the idle circuit is separated, which is why idle RPM remains unchanged.
(If you twiddle the full-load setting internally, there is a different internal idle adjustment that needs to be tweaked, as the full-load moves the whole rack. The ALDA may also need to be adjusted *leaner* if you do this, especially if adjusted towards the max capacity of the pump, about 20% above stock settings.)