I had some trouble with the logic of this puzzle in my head, and the visuals were too large to realistically render for me to spot-check my solution, so I kept getting part 2 wrong. I eventually realized what needed to be done to get the right answer, which was partially the realization that I needed to check +99 instead of +100, and partially that I probably didn't need to check the entire space, just the bounding points, at least for the initial filters.
And then I optimized it with a bisect instead of a linear search. Always a good idea when you need to narrow a large range to a single point.