armor damage

I just created a new datapack with custom armors that are supposed to be more durable than diamond, and it works. But those same armors have different armor values — for example, obsidian has a total armor value of 22 (diamond is 20), and topaz has a total of 28. However, both the topaz armor and the obsidian armor take the same number of hits to die, even though there should be a difference. I’m using a weapon with 9.5 attack damage. (1.21.9/10)