In the Top Menu a slider on the sharpen icon (<->)
to control the threshold border for the sharpen option.
Could there also be a threshold slider if the mask is blurred, so that you can define up to what border the facegroup is created - so that you can possibly cut off the blurred part of the mask. Like the blur top menu slider (blur ->) for the tap to facegroup option (<-> on tap) slide left right for the threshold…