Looking at this issue from a different perspective, there is a lesson from the field of modern military science that occurs to me. It goes something like this in order of priority for the soldier:
1 don't be there (be aware where the enemy is looking and avoid them)
2 don't be seen by the enemy (use camouflage & concealment)
3 don't be hit by the enemy (take cover - manouvre)
4 don't let the round penetrate (body armor)
5 don't let the round kill (highest protection to most vital spots)
Ok so this goes beyond a discussion of armor protection (which is really point 4) but perhaps some of the relative benefits of different armor are that they aid in points 1, 2, 3 and 5. So the rough ranger with the weather-worn hide may score low on point 4, but he scores a lot higher on 2 and 3 than his mate in field plate.
