Custom Fire Protection Won't Let Players Die?

I'm making a mod that adds new late-game armors with their own gimmicks, and to balance it out, I'm making netherite have built-in fire protection without the enchantment. It works almost perfectly, but the issue is, when you get down to half a heart from lava or fire damage, it can't kill you.

To achieve the fire protection effect, I made it heal you for [amount] / 20 per piece of netherite armor, reducing fire damage by 5% per piece. Yet for some reason, you can't die, even if you only wear one piece of armor. ?????????????????

Please help :(