Less deliveries per km = less deliveries per hour = higher cost Pretty simple really. And some deliveries e.g. NZ Couriers do not use the mailman.  

Kevin You can courier across Islands, for next day delivery, a very small item for a bit more than $5.50 but a whole lot less than $19.62, if you use pre-paid track packs.

Check the Address for a specified courier: https://www.nzcouriers.co.nz/address_checker.html https://www.courierpost.co.nz/tools/address-checker/ https://www.nzpost.co.nz/tools/address-postcode-finder Different couriers have different categories.