I like the size of the category images in your demo site, but on my site http://hazelcombefarm.com.au/?post_type=product they appear a lot larger. I just can’t work out how to make them smaller.
It happens since you enlarge the products container and remove the sidebar area. But, each item width remains one third of the container. Maybe you would need 4 columns instead of 3? If so, you can follow this solution.