Step one, make your shadow mask. Step two, from the shadow mask make a highlight mask. Step three, the sandwich of your two mask will allow you to control the middle tones.
For those imposible to print negatives masking is the best solution. I guess for good negatives it could be an advantage the way you plan to use them, but wouldn't it be better to use a long scale paper like Azo in amidol instead of doing all these masks? After all what you are doing is fitting the negative to the paper scale and all of what the masks do is either "lenghten" or "shorten" the particular area you are working on. OTOH if you are doing enlargements I can see how this would not be practical.Anyways Hope this helps.
I do agree with you, when used well masking can produce some of the best prints.