From what I've learned the "OPACITY_BASE" is for changing opacity, as it look like and "OPACITY_VELOCITY_BASE" is for changing duration. Settings really depends on what is your custom smoke settings, like if you turned AC smoke on or just let the Content Manager custom smoke turned on. So yeah it's kinda hard to experiment without direct images.
From what I've learned the "OPACITY_BASE" is for changing opacity, as it look like and "OPACITY_VELOCITY_BASE" is for changing duration. Settings really depends on what is your custom smoke settings, like if you turned AC smoke on or just let the Content Manager custom smoke turned on. So yeah it's kinda hard to experiment without direct images.