So I almost got it: you can reconfigure the graph height before rendering by calling the `configure()` method, and then set the right graph height depending on the legend height. Like this:

https://github.com/prometheus/promdash/commit/58ef0bd90f2c29bf2f77a793d21a32a626a25496

Now the graph looks right, but the problem that remains is that of the hover legends not being vertically aligned with their series anymore...