QTR-Quadtone RIP

Let's say we make a new image in 16-bit grayscale with a Gamma 2.2 profile, and create a step-wedge with 11 steps. We get an image whose K values go 0, 10, 20... 100. Fine.

However, if we mouse over the other patches, we see some discrepancies between the K value and the HSB B value. For example, the middle patch shows a K value of 50%, but the B value is 58%. Similarly, where K = 10%, B = 92%. 

Why aren't these two measures simply the compliment of one another ?  

Which system is appropriate for making a step wedge, when calibrating with QTR ?