I think the difficulty setting should work like this:
Easy:
HP of the player characters 125%
HP of the enemies 75%
Cooldown of enemy skills +2 turns
Normal:
HP of the player characters 100%
HP of the enemies 100%
Cooldown of enemy skills +0 turns
Hard:
HP of the player characters 75%
HP of the enemies 125%
Cooldown of enemy skills -2 turns
General Easy-Med-Hard difficulties are perhaps one of the easiest things to mod in the game. There are setting for all 3. Aprox 75 settings for players and NPC's for each difficulty level. You could so something very close and perhaps feather in a few more tweaks.
You unpak Main
Open characters.xslm in excel
From there it is pretty straight forward, save.
Then open All.xslm, click the Generate button.
It creates and updated characters.txt file you place in a mod folder (will supply details if one is interested in actually do this)
Play game with new settings.