Aust Post Package Calculator Extension problem

Hi,

I have bought the Aust Post parcel calculator.

I have the API from Aust Post and set it up and enables it in OC.

I have tested an product however the extension gives a different figure than the Aust Post Web site calculator at.
http://auspost.com.au/apps/postage-calculator.html#tab2

My product us 48 x 17 x 22 cm - 2.5 kgs going from 2170 to 2444

Only options selected in extension are Regular Post - Signature on Del.

Only other shipping enabled is Pick up from store.

I get $20.79 from the extension and Aust Post says Regular $16.40 and Next day $28.30

Any ideas what may cause this or to correct it.

Thanks

oz

Version? What did the author of the calculator have to say?