Yes, it’s called “Ink Calibration” in QTRgui. I use 50% or lower for plain paper. More than that is likely to overload the paper and cause it to buckle.
Your instructions for printing a purge pattern from Windows say “Select 100% saturation if printing on heavyweight, coated/print paper or 50-80% if printing on uncoated, very thin or typing paper.” I don’t see a slider called “saturation” in QTRGui. I do see a slider called “Ink Calibration.” Is that it? FYI I am printing on typing paper.