How to offer Express Post Platinum Parcel

When I processed C&S parcel today one of the postage options was Express Post Platinum Parcel.  I have today listed another item and thought I might as well offer this service as another option, considering that somebody might BIN it and want it for Xmas, but when I selected express parcel (the only express option) it came up the same price as the C&S with signature.  That is not right; within Victoria the signature C&S is $11.80 and the platinum express was $17something, and for interstate it should be about $50+ - so how can you offer it?

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Voltaire: “Those Who Can Make You Believe Absurdities, Can Make You Commit Atrocities” .