Here's the thing I came-up with to experiment with different shapes:

https://shapedveins.artfly.io/

I first became aware of this technique from Dan Shiffman's Coding Train Coding Challenge:

And that led me on to find an excellent article and Github project by Jason Webb

• Article: https://medium.com/@jason.webb/space-colonization-algorithm-in-javascript-6f683b743dc5
• Demos: https://jasonwebb.github.io/2d-space-colonization-experiments/
• Code: https://github.com/jasonwebb/2d-space-colonization-experiments

My first attempt using Jason's code:

I was so beguiled by the technique that I spent quite a while digging into the code and setting up a version to experiment with:

https://shapedveins.artfly.io/