The percentage will ALWAYS be from 0 to 1. You can only do the math to calculate your big numbers down to a range from 0 to 1.
The normal way is to divide your CurrentHealth by the MaxHealth.
For example CurrentHealth = 50, MaxHealth = 100 -> 50/100 = 0.5
Other example CurrentHealth = 120, MaxHealth = 200 -> 120/200 = 0.6
And so on. What exactly CurrentHealth and MaxHealth are, depends on you.
Fall Damage etc is applied to the CurrentHealth. So if you have CurrentHealth = 120 and MaxHealth = 200 and you fall too far and get 20 damage,
you will end up with Currenthealth = 100 and MaxHealth still = 200. So you have 100/200 = 0.5.
That’s how it works and that’s how it needs to be done. You can’t change the way the PercentageBar fills with 0 to 1.