... how they affect each tonal zone of the preview mainly due to their gradual blending in to each other to where I can't see where one stops and the other starts within each zone they act on...
Probably because the relationship between sliders is dynamic and inter-dependent, i.e., each slider's effect depends not only on how far you push it, but also on the position of other sliders. That assures smooth and gradual tonal transitions, a great part of why PV 2012 is so superior to the previous ones.