Discount does not count the entire cart quantity

I'm trying to use the "Simple Discount using the VAT Hack" (http://www.drupalcommerce.org/node/461) to provide a discount on the purchase of 12 or more items.

This is working great as long as there is one product type in the cart that meets the 12+ quantity condition. But, if I have two different products and have the combined quantity of both products meet the criteria (for example 5 of one product and 7 of another), the discount does not show up.

How do I make it so that the discount considers the combined cart quantity of products, not just a single product or line item? What condition do I need to set to make this happen?

Thank you,

Posted: May 31, 2012