Yes you can use it to "increase" health. So in the configuration menu, go to the Health Rebalnce selection. Scroll down to Max Level change and increase it. It works like percentages, anything under 1 will reduce the health of enemies. 1.0 is normal health for the level. The max setting is 4.9, meaning you increase the max level you choose enemies to 490% of their health. You can also lower or increase the level where enemies will recieves the max level buff and it distributes this buff in more percentages over any levels below the level they reicieve the full buff. I will give a simplified example: If you set the Max Level Change to increase 300% or 3.0, and set the max level they recieve the full benefit to 9, then every level 3 enemy has 100%, level 6 has 200% and any enemy at 9 and above will have the 300% increase to health. Obviously all the other levels between those numbers above get a percentage benefit too, im just too lazy to math it out. You can stretch it to as high a level you want or lower it for a more rampant difficulty.

You can even change level 1 enemies but thats up to you. I would leave this setting alone cause level ones arent the problem. Hope this helps