You understand the ink limits which is good.
The Gray Val settings determine the partitioning of the black ink. Basically, if you put the gray highlight and gray shadow settings at 0, you should reproduce the K ink calibration ramp with the 3 partitioned inks. With that as a basis for the gray ramp you can reshape it with the gray curve settings (see below).
I would throw out all your copy curves for each of the color inks. When you add more ink to the LK and LLK ramps you are effectively changing the partitioning points which can throw off your linearization. It would be a better bet to just use them as a Curve_INK="0:100" if you are worried about filling in the printer dots. With those all as straight line ramps separate from the gray inks you can do the linearization with the gray_curve= setting using this free tool I created a few years ago (again, sorry you wasted your time with Ron's handmade linearization stuff).
I do remote Skype lessons on all things QTR and digital editing through my site below if you would like to see all this in more detail on a one-on-one basis.