Zone Rates Estimate Shipping Calculation?

I'm confused by the way Zone Rates estimates are being calculated.

I have set the following:
Module>Shipping

• Calculate Method: by weight.
• Zone 1 Shipping Table: 0.5:3.00,1:4.50,1.5:6.00,2:7.50,3:9.00,4:10.5,5:12.00,10:30.00
  Configuration>Shipping/Packaging:
• Package Tare (both for small to medium and larger packages): 0
• Enter the maximum package weight you will ship: 10 kg

I have tried this out with an item weighing 0.9 kg and increased the quantity +1 unit at a time. All goes fine until I input 12 units, which amount to 10.8 kg total. The total shows $60.00 (2 boxes of 10kg I suppose). I would have thought that it would total $34.50, which is $30.00 (one box of 10kg) + $4.50 (one box of 1 kg).

If I increase the maximum package weight to 11kg, then the total becomes $35.

How does the estimator works?

Thanks much!

Actually, you should be getting:
2 x 30.00 = $60.00

The Tare Rates, set to 0:0 ... does that change anything?

The Zone Rates does not use the weights based on box size in the manner you are thinking ...

Once the maximum definition is reached, that is the amount used per box ...

The tares are already set on 0:0. I tried and enter some values but the end result was the same. If over the maximum package weight, the estimator will assume it's twice the maximum package weight.

I guess I will have to enter a maximum package weight I will NEVER ship, say 50 kg, and then enter incremental values from 0.1kg to 50 kg under Zone Shipping tables.

Thanks for your reply.