Just my 2 cents, but one reason for the greenware running more might be that greenware doesn't "soak up" the glaze as much as fired bisque and so leaves more on the surface to run later when fired. Also, you did mention firing at 04 instead of the recommended 06 - I've found that even a very small temperature change can have a big effect on the glze with both low fire and high fire glazes.
Thank you! What is the firing schedule for single fire? Is it the same as a regular cone 5-6 ? Do you do it slower as far as ramping temp? Thank you for sharing
