Exclude Shipping Class

Hi,
I am using Advanced Free Shipping to offer Free Shipping across all products on our website, when a customer spends over $300 and is in a Metro area. This works flawlessly.
However, I have a specific product which only attracts Free Shipping when the spend is over $2000. I have set this up in the AFS plugin, with its own Shipping Class, but it is being overridden by the ‘free shipping to Metro over $300’.
I have given this product its own Shipping Class, but how do I exclude this shipping class from the ‘Free Metro over $300’?

Thanks in advance