Headphones monitor mixer

I understand the section well, but if I go below the level of track # 16 (SMPTE), in order not to hear it on Headphones, SMPTE does not come out for physical output # 16.
So, the “PRE or POST fader” option, I do not experience any changes to the system.
Whenever I get down to -inf level # 16 (SMPTE), nothing comes out of the physical output # 16. Although I select PRE or POST in uTool2 mixer.