You can use the "density" URL variable to multiply the number of volumetric raindrops, like so:
https://rezmason.github.io/matrix/?volumetric=true&density=3...
The full list of parameters is in the README.md at:
https://github.com/Rezmason/matrix#readme
The similarities you point out are probably because of my recovery of the original font, which is also in the repo, and may soon need some expansion :D