They don't really work like that Ed, no auto adjust, hence the adjustment knob. Mine were underfilled too, still are but I just throw new pads in when they run out of adjustment. There's not a massive volume of oil to play with or a reservoir so could be susceptible to differences in factory fills.
ive had the exact opposite problem with these brakes.
the gap between the (new) pads and the disc is cavernous! could park a whole other bicycle in there. do i need to get some more oil into them?