QTR-Quadtone RIP

I am extremely new to using Quadtone.  It came highly recommended.  I 
have an Epson 2200 printer.  My question:  What is the best blend 
setting to get a truly neutral black?  Lets use Premium Lustre paper 
as an example.  When you adjust the slider to, say, 75, does that mean 
the right curve is dominant or the left curve?  Any and all advise 
will be and is greatly appreciated.  Thanks.