Resistance V (5) = Resistance IV (4)

I was testing the resistance effect for something important and I noticed that resistance V(5) Take's the same amount of Damage than Resistance IV(4).

 

What I expected to happen is that resistance V(5) makes me takes less damage than Resistance IV(4)

 

What actually happened is that they both take me the same amount of damage.

resistance IV(4) is equal to diamond/netherite armor, so for some reason resistance V(5) is equal to diamond/netherite armor too

Resistance IV(4) gives you 80% more protection, but Resistance V(5) also gives you 80% protection too for no reason. so the conclusion is it should be that Resistance V(5) gives you 100% more protection, not 80%. please fix this and thank you.                                                                                                                                                                      (also the numbers next to the roman numerals represent what number is the roman numeral, NOT the amplifier)