Regeneration not working correctly

I'm trying to enhance the combat system in vanilla, so I try to use regeneration while not in combat and it turns out it doesn't work when naturalRegeneration is false or normally.

Steps to produce:
1. Harm your self
2. Type in the following command
effect (username) 10 60 1
3. Wait a moment
4. You'll see that it doesn't effect your health regen overtime, only natural regen works