How is the Best for Military Score Calculated

Wololo guys, I aged up from Iron Age to Imperial Age.

So here is my question, how is the “best” for military score is calculated? It always make me confused.

For the circle to the left, it says unit lost (the lower the better), which normally no one will have 0 casualties, but is it rewarded as the best score?
Same for the right, for losing buildings, why 0 is not the best score, but 3 is???

Please let me know the thoughts and I go back to Wololo.