As you get lower in range, you have less discrete tone values to work with, however, reasonably modern cameras have at least a 14 bit ADC, and scanners are 16 bits, so if you place the minimum density at the maximum ADC value, the maximum density will usually happen well before you run out of ADC range and you’ll have more discrete tone values to work with in the shadows. There is ADC noise down there, but again, if you maximize signal to noise by putting the minimum density as high as it’ll go without clipping anything, the noise on the low end is reasonably minimized for a single capture.