Well, This script would help you link positional data to a mask vertice. Unfortunatly its kind expensive if you need for just that example. There are others scripts there that work/assist with masks there are “name your own price” and may be able to assist you.
For example Keytweak would help you interpolate masks to visually give that “falloff”.
Edit: Thinking about it now, You may be able to pull that out with a line and puppet tools, if not actually needing a mask is an option. You can easily link a puppet point to your tracked mask with the pickwip.