QTR-Quadtone RIP

Hi to you all,

I'm kind of a newbie with quadtone rip; if I'll ask you questions
someone already answered, please redirect me to the thread (I've made
a little search but with no great results).

Here is my setup: K6 quadblack inks from Piezography with EP7000
printer, EyeOne Pro spectrophotometer; I'm trying to create a custom
curve and linearization, following the pdf instructions.
My doubts start as it suggest how to measure the relative ink
densities. I did it his way, here is a little example:
 
1. I've measured the K100% (L*17,4)
2. I've measured the C100%, M100% and so on (actually they're not
Cyan, Magenta etc. but gray shadows, I'll call them C,M,Y,lC,lM to be
clearer). Let's say that C100% is L*23,9
3. I've found that the nearest patches in the K 21 steps are the 40%
(L*26,0) and the 45% L*23,3)
4. Doing little math, I've used the Y=aX+b equation to find the
interpolate % between 40% and 45% that gives me L*=C100%=23,9 and
eventually I've found C100%=K44,78%.
5. I've done it for all the 6 inks.
6. I could have been using Density instead of L*, but numbers
shouldn't change: D=((L+16)/116)^3

And that's OK. 
But...

Does it really make sense to look for the nearest printed K patch? I
mean: in order to find the relative ink density, wouldn't be better to
do not rely on the 0%,5%,10%... 95%,100% K scale (printed with no
linearisation, no known gamma), and use only the 100% patches?
I can do this:
1. Measure the K100% (L*17,4) and calculate Density= 1,63
2. Measure the C100% (L*23,9) and calculate Density= 1,39
3. Write the proportion 100:1,63=X:1,39 so X=85,3%
That seems to me a much logical way to find relative density. And the
value is so different.

Maybe I'm wrong, I'll be glad to hear from you experienced users your
comments and suggestions.
Best regards,

  Davide