It took me a while to understand what to do. After I did, I realized that it is quite difficult, because if you move a tad early or late, you make it far worse. This leaves no cognitive capacity to keep an eye on the right portion of the screen.
I would suggest a more "forgiving" control over the line, where pulling the line in the opposite direction a bit in front or behind a spike lowers the spike as well. Maybe a wider area around the cursor being affected by it?