Another way to calculate this chart.
Each dice has an average result of: (its lower result + its maximum result) / 2. Which gives:
So, when two dice are rolled, the two 0.5 become a 1, which explains the + 1 in the formula: (maximum result of the two dice / 2) + 1
When only one die is rolled (innate defense or defense without the good skill: "D0"), or when three dice are rolled instead of two (characteristic or skill of D12+D2 or above), the result is not anymore a whole number.
D8 + D12+D2: 4.5 + 6.5 + 1.5 = 12.5
The result has to be rounded, then. Down, if the GM wants to be kind with his players, or up, if he wants to give them a bigger challenge.