Allow Front Base in CustomPress doesn't seem to do anything and I need it to!

Our site sells custom canvas art prints. We have a custom post type called "Canvas Art Prints". We have some custom taxonomies too - color, artist, type, and style.

We used the taxonomies to create some menus that link to archive pages and they work beautifully.

The urls look like "spiffyhippo.com/color/red". We want them to look like "spiffyhippo.com/canvas-art/color/red". I thought the "Allow Front Base" checkbox would do the trick but nothing. Then again it doesn't do anything if it isn't check either.

Will you give me an example of when and how to apply "Allow Front Base"?

We plan on creating another custom post type called "Framed Art Prints" and I already see a url nightmare approaching.

Thanks.