Put it another way - imagine a super bloody war with 1 million soldiers who all killed each other. You have 1 million kills, divided by the 1 million soldiers, creating a 1.0 soldier kill rate.

If any soldiers survived, the rate drops. Obviously you can get a number above 1 if you place civilian deaths in the numerator but not denominator; but in the "ideal" war where civilians are safe it can't exceed 1.