we created an advanced rain damage system

Hello, I'm facing a difficulty in creating a mod where the intention is to cause damage when it rains to players and entities that are not a zombie, and the only way to avoid this is by using armor in the helmet slot or staying under a block (which would theoretically be a place where the player and other mobs don't get wet), I tried several methods but most of the time the system of not taking damage when under a block doesn't work or using the item in the armor slot.