Just a note to inform that (to the best of my knowledge) shipping dimensions do influence postage costs.

For parcels exceeding 1kg 'actual' weight, AusPost assesses based upon 'Actual' or 'Cubic' weight: Whichever is greater. Cubic weight is LxWxH(m) x250.
I ship large, lightweight items and I find this policy is enforced at my LPO. The eDeliver DRC should be taking this into account when it returns postage costs.

I'm not currently using Ubercart but this may be relevant to those creating/using this module.