QTR-Quadtone RIP

I've been playing with variations on Roark's Eboni 6 (strictly speaking carbon 6 since I am using Roark's E6B base) with a 1430 (1400 family).

Why should my K ink be 100% Eboni? Even printing black only I can get the same DMax (on Epson Hot Press natural) with a diluted K, say 90% or even 86%. 

A more dilute K should force the printer to use larger drops which gives a more neutral tone (according to Roark's tests).

More generally, when designing an Eboni ink set, is there a rule for determining what dilutions to use? With the standard (100, 30, 18, 9, 6, 2) I find that the inks do not give evenly separated value / density curves but have gaps (eg. K and C) and nearly overlapping curves (e.g. Y and LM). While with 86, 40, 18, 12, 9, 2 the curves are more evenly separated which should make it easier to partition between inks.

Thank you,

Vincent Wan