13x13 (169) is roughly twice as many intersections as 9x9 (81), 19x19 (361) is twice is large as 13x13, and 27x27 (729) is twice as large as 19x19. It would be interesting to experiment with this board size.
Wouldn’t it be better to focus our efforts on building a small community of 21 x 21 players?
Let’s do that too! I created a Large Board group: https://online-go.com/group/4730