Just to note that my professional printing 'career' (sounds good, but was only two years until the company downsized, concentrating on E6 and RA4 and dropping B+W) was based on a De Vere 504 with the usual Dichromat diffusion head. Then and now, I can see no reason to try to set up 'grades' for variable-contrast printing.
The speed-equivalent point is true for only one shade of grey -- the majority of the photograph will, obviously, not be that shade. A difference of a tenth of a stop of exposure is visible on the print, so changing contrast will almost always require exposure adjustment if you print the whole image in some notional 'grade' of contrast.
For any sort of complex neg, I suggest exposing the print as one lower contrast grade (try equal yellow and magenta, about 30 units) and then adding density with more magenta where it is needed. If the neg needs lower contrast, then start lower. Thinking of adding (or removing, implying you need a different base exposure) contrast here and there, instead of sticking to some imaginary contrast-grade, is much more flexible and intuitive.