Your math is wrong because if you’re not looking at overall civilian casualty rate then you need to remove the allied combatants from the denominator. The Pentagon leaks have a break down that has both civilian casualty numbers and enemy forces. 66,081 civilians were killed compared to 23,984 enemy forces. If the US killed 36% of all the civilians they’d be at 1-1. Which is roughly the rate the Iraq Body Count attributes to them.