Hey there Shaun -
Eli here from the Shopify guru team. This is a great question, and one that - until recently - I didn't have as good an answer for as I'm happy to have now! Due to a particularly great app developer, Atom Yard, storeowners can download a tool called Better Shipping: https://apps.shopify.com/better-shipping
Provided you have the Carrier Calculated Shipping option enabled, Better Shipping allows you to customize your shipping rates based on more refined ZIP and Postcode parameters.
Let me know if this hones in on your question!
Cheers,