I agree i feel a 13x13 is a good compromise between the sharpness of the 9x9 and the grass lands of a 19x19. Considering that you play a bot 10k i find the evaluation quite efficient and worthy. Looks hard to beat with 4 without a little bit of practice, and with 3 without a bit of theory and ideas.
Most interesting discovery is that you’ll need just 1 game for a beginner to get his diploma.
There is less space to do something as 25 stones on a 19x19 IMHO.
Anyway on OGS it seems that