QTR-Quadtone RIP

I am making a profile for Epson Velvet Fine Art on Epson 2200.  
Percent ink, L* values for black ink of the calibration target:

0,98.7
5,74
10,59.3
15,48.7
20,38.3
25,33.2
30,29.4
35,27.6
40,25.3
45,23.3
50,21.6
55,20.5
60,19.6
65,18.3
70,17.7
75,17.1
80,16.7
85,16.3
90,15.8
95,15.4
100,15.4

Question:  where would you put the ink limit based on these data, and why?

Thanks.

--John