I'm currently doing a variation test with different media types, same problem is recurring, I understand the media types or the rough art of guessing, but I use the same media types when profiling and colour work and the results are perfect. I'm going to try your suggestion when I better understand the process - I'm reading the http://www.outbackphoto.com/artof_b_w/bw_09/essay.html
at the moment. I'm also in touch with Velmex UK trying to solve the problem and they're preplexed but very helpful. Curiously this problem I'm having might be related to another which happens rarely but is a nuisance when it does, very occasionally print comes out with strong banding, then if another image is sent to print the problem get worse till its just a ghost of an image on horribly expensive paper! Quick solution to this problem was to change media type, print on a cheap paper, turn off printer and turn on again after a few minutes and then the printer is back to normal. I've check for clogged ink heads and they are perfect every time so I think this is a driver problem. I had to do about 1500 mono prints last month at that problem occurred after every 30 - 50 prints
I can achieve good results with custom profiles but this printer is capable of better and consistancy is important.
Did you try the method I suggested? One other thought--if the wrong media type is selected and too much ink is being laid down for that particular paper there may be a lack of differentiation in the darkest tones that even the QTR B&W profiling won't solve.