I can definitely agree with everyone else that a stronger dilution of LD20 than recommended helps; I can't remember what I settled on for the lith print exchange, but it was around 1:20. At the lower dilutions the highlights and midtones were a beautiful pink colour (on Fotospeed lith paper) but actually getting any infectious development going to bring out the shadow tones was an exercise in frustration.
At the around 1:20 dilution, the blacks did start to rapidly develop, although they never fully blocked up, leaving a nice speckly appearance in the shadows. (Speckled Jim keeps popping into my head now...)
I put my troubles at the recommended dilution down to my own incompetence, so actually quite pleased I don't seem to be alone ;-).