QTR-Quadtone RIP

I am working on a QTR curve using carbon sepia piezotone inks and am 
now comparing my linearized curve to the ideal density chart.  First 
question is how close should the values match?  Second question, if 
the values are off, what is the best method for trying to get a better 
match?

For example, if the ideal density at 50% with a dmax of 1.75 is .601 --
 what do you do if your density is .640?  Do you apply a general 
correction by using the gray curve sliders (highlight and shadow) or 
is there another method that is more specific?  Or do you just not 
sweat it?

Thanks,

Jenny