QTR-Quadtone RIP

When figuring the relative densities do you figure them all relative
to K or to the next darkest gray?  I'm using UT7 ink with a 2200 on a
PC and have made cool and warm curves measuring all the ink densities
against K  but I read here, I think, that it might be wrong.  I've
reread Tom Moore's excellent user guide but am not clear.  The prints
I'm making now are the best I've done so it measuring against K can't
be too far off.

Thanks,

Tom