The firepower is important to a degree, but what really pushes the CV up or down are passed/failed rolls after the combat phase. Checks are made against leaders morale and inf/mech ratings, and additionally against units morale and experience. These are the main variance generators, fluctuating CV from 1/16 to 16 (not 100% sure on the numbers) times the starting value. I suppose the distribution is normal(ish) but not discrete - it has big cliffs at the multiples of 2.
The combat phase throws away some elements from the initial setup (due to destruction or suppression), but the CV phase does the job.
In order (German slant) -- Stukas, Nebel's (Rgt), 210mm, 105mm Howitzers will turn a battle.
If you are agasint soft squads and no opposing guns (or a lot less) the quad 20mm directly attached can change a battle. I readily exchanged 20mm quad devices for much cav in the German winter offense.
A disrupted sqaud or device counts zero toward the CV.
Except for optimzing leaders I admit I have not considered the post battle leadership checks in calculating final CV. I will have to try and understand this more. I have spent a great deal of time at the highest message level and taking notes about the ranges, activites, and vulnerablites of sqauds and devices.
"What gets us into trouble is not what we don't know. It's what we know for sure that just ain't so"