confused about armor protection and natural protection

[Norfleet]

Some items, like the invulnerability spell, don't increase protection, they set it: So if you're affected by Invulnerability, Robe of Invulnerability, or maybe the Amon Hotep, anything which fails to increase your protection over 30 has no effect, and anything which increases your protection to or over 30 makes invulnerability irrelevant: They're not an armor effect, they're simply if prot < 30, prot = 30.