Reflection densitometry is an exact science. The mid scale variations are a measure of contrast, not the Dmax. Dmax is limited by the laws of physics causing it to fall between 1.8 and 2.2 depending on surface. In normal viewing conditions, this range can be seen, but anything over that, visible by transmission, is not seen by reflected light. This goes for color or B&W. However, again due to the laws of physics, in color there is a slight hue shift past the reflection cutoff limit.

So, you can trust reflection readings with most any good densitometer. At EK in KRL, we used Macbeth units.

PE