Is it possible to make brushes thinner than 1 grid square? I heard somewhere that you can edit the proportions from a special menu, but I'm not sure where.
I didn't make it!
You can go down to 0.5 and 0.25, but these will get cleaned up by the editor upon restart or brush cleanup.
What are you using this for? Because you could always turn the small brushes into an .ase model and then import them into your map... (p.s. I would check the paths before using the batch file)