When barbarians spawn. The health of the barbarian doesn't take into effect the horde difficulty. The change will cause the health of the spawn barbarian to reflect the difficulty settings from the config. So they will start with less health with the difficulty is set to 1 vs. 10.
barbarianHordeDifficulty = 1 - 10

This will be a percentage of what the game is asking for with a min. health for each. Can't have barbarians being spawned with 1 heart.
There is no max. a value of 10 = 100% of what the game is asking for.