Additionally, it seems that as the graph spreads to the right it disappears outside of the div and I can't find any way to click or scroll to keep following it horizontally.
I had reported this sometime back, but was turned down: https://github.com/HackerNews/HN/issues/78
One thing: you should increase the minimum size of the smallest sized clickable circles. They're hard to click on to expand.
This will ensure that the area, which is proportional to the square of the radius, remains proportional to the size.