Grid size (hidden settings)

In the game configuration file, located at
there is a line that controls whether the hidden setting is displayed in game's settings menu:

If the file GameUserSettings.ini is not present, try to launch the game at least once and check again.

In order to enable the hidden grid size setting, change the value to True and save the file:

After that, a new option will appear in Gameplay menu:

In the game, the difference will look like this: