I agree. Someone put it brilliantly on reddit:

Spokesperson: We are pleased to report that we have encircled the Carthaginian 5th Army and decisively destroyed their entire invasion force, including eighteen regiments of motorized rifles and their 2nd carrier battle group. Casualty numbers are still being tabulated, but current estimates indicate that we lost about a thousand troops while inflicting twenty-thousand casualties on the enemy.

Reporter 1: The British people demand accountability, ma'am. This victory in the only large battle of the war in no way compensates for the defeats of the previous six months. What about the retreat of the 7th Dragoons? What about the retreat of the 1st Carrier Battle Group? What about the retreat of the 5th Infantry Division?

Spokesperson: We would like to emphasize that we have taken less than a hundred casualties in the past six months.

Reporter 1: But those troops retreated from battle, instead of being slaughtered to a man! The British people desire an end to this conflict, regardless of what demands the enemy might impose upon us. Cede London to the Carthaginians, else there will be uprisings in the streets!

Spokesperson: You wouldn't happen to be a Carthaginian covert operative, would you?

Reporter 2: Ms. Spokesperson, I'm with the London Times. Our readers have been clamoring to hear the tale of the Battle of 17 Easting, where our glorious 1st Army encircled and entirely destroyed a company of one hundred Carthaginian infantrymen equipped with muskets.

Spokesperson: Well, I'm sure that the 1st Army -

Reporter 2: The British people love our heroes. Stories of the heroic way that the 7th Air Wing dropped over six thousand pounds of laser-guided precision bombs on the hapless Carthaginian musketeers, before the 7th Royal Armored Corps valorously rolled twenty Challenger tanks over their corpses, have truly inspired our people to believe that we can win this justified war!

I would say

Enemies eliminated/retreated v. Overall enemy army Strength

AND

Enemies Eliminated v. Your Loses

So if the enemy army is big, or you lost a lot in the victory the War support gained/lost is small, (say +-2) but if you Wiped out their entire army with no losses its large (say +-20)