Digital BW, The Print

Today I've been printing a 75% all black image on my Epson 7000. I have the 
standard Hextone inks with VM HEX-4-K in the black position. 
I believe Paul R. tested this as his favorite and piezo equal in the black 
position.
Is VM-HEX-4-K The best black to compare to Piezo?
What I can tell you is that visually this black is a full stop lighter than 
Piezo black.
Compared to the Piezo print of the same image. This MIS black looks more like 
80-90%. Its not a work flow issue either as I printed a black only image also 
with the MIS and its still weak compared to piezo. Is this because I dont 
have the Vari tone inkset included with this black? Are you guys getting some 
blue in there and making the black appear darker?
The More I use MIS inks the More different they are compared to Piezo, and 
black Vs black Piezo wins hands down. Maybe MIS ink just doesn't like Royal 
plush/ or Jazz paper!
Thats a possibility. Can anybody else explain my poor MIS blacks while know 
one else is complaining?
Steve Meyers