[Jefferson3000]

Air Freight delivery zones are not arbitrary. They were set up by an organization called ACI. This organization is no longer an entity, but up until a few tyears ago, they published a list of freight rates for different airport cities.. They were organized in the fifties to help freight forwarders know what the going rate for a specific airport region would be. They are not based on mileage alone, but tonnage. If you PM me, I might be able to sort this out for you.

Oh, and if this is your method of determining local rates, yes, you should most definitely dim the freight.