You should probably ask this question on the QTR yahoo user group. In past conversations with Roy, the inventor of QTR, he has said they he has tried to eliminate the use of yellow in "warm" curves with Epson Ultrachrome ink, since it was the weakest link, but also mentioned that the sepia setting did use quite a bit of yellow. QTR warm and neutral settings use as little color toning pigment as possible. ABW uses a lot more color ink, but still has pretty good test results as long as the prints are not using a lot of yellow.
Now with the new Epson inkset the yellow channel has been improved significantly, so it seems this should help even sepia prints a lot. The new P10K and P20K printers also have an additional light gray so hopefully even less color inks are needed for composite grays. Epson has said almost nothing about this inkset in a practical way so we'll all have to wait until independent tests are done as people are using them. Epson should have designed a way to use this quad gray inkset in all of their new printers, as an option, but they didn't. I wouldn't have been hard for them to create a software adaption for replacing one of the additional color inks they offer, but they didn't.
Your are right that there is nothing there about usage though it's clear that the sepia tone will use more colored ink that the neutral (probably yellow). I just pointed you to the test set as you can see what the stability of the various shades of gray are for the different settings. I print ABW on my 3880 and use a QTR generated profile with it. One can still do this under WinOS but not MacOS.