Can't the NPC confidence and health relation be made non-linear, i.e., At full health, confidence is 95. At half health, confidence is reduced to 30 (or another low number)?
I guess it could but I'm wondering what the purpose would be. The only point of the Confidence stat is to determine how much Health an Actor has to lose before they run away. With your example, the NPC at 100% Health has 95 Confidence and therefore isn't running away, but at 50% Health has 30 Confidence and therefore runs away (because it's lost a higher percentage of health than its Confidence). If the goal was to make the NPC run away at 50% Health, then their Confidence could just be set at 50 the whole time.