It's a bit of a long story but to cut to the chase, we're installing a shower and the shower doors are going to need some wood to screw into. The vertical part of the vent (A) is right in the way of us sistering a stud to an adjacent stud. The sistered stud would provide the base for the shower door. So, I thought if I could move the assembly down a bit (reducing A) , I could sister part of a stud above the vent and then sister another against that, that would reach the bottom plate. (Forming a kind of a stud bridge over the relocated vent). That's kind of hard to describe....
If I did that though the new vent connection would be below the drain holes of the bathroom sinks, thus violating your specs.
But, with a bit more work, I think I can just move the whole shooting match to the right without changing any heights of connections. The vertical 'culprit' part of the vent would then be out of the way. Thanks for any further hints.