I looked at this question, but it only answers part of my problem. I want to create Thiessen polygons based off of the green points within the blue polygon boundary ONLY. I've set the Processing extent to the exchange boundary, and have set the raster analysis mask to the same exchange boundary.
When I run the Thiessen polygons tool, it will still use the largest extent of the polygon, not the actual borders of the polygon. You can see that polygons are created for points outside of the blue border. Is there a step I'm missing?