If someone invades my home, 75% of people in my home are my family including the invader. So if in response, I only kill 50% of my family, by your logic I would have done very well.
The fact that they are killing a percentage of civilians that's less than the overall percentage of civilians in a region is irrelevant to determining how effectively civilian harm is being minimised, it just means they are doing slightly better than killing people completely at random. I think you'd agree that's quite a low bar you're setting there.