Question about a feat from Monster Codex

[Palthinon]

"Tough as lron
Effects that grant natural armor work even better for you.
Prerequisites: Toughness, duergar.
Benefi: When you gain an enhancement bonus to your
natural armor, that bonus increases by 2. This has no effect
ifyour natural armor bonus is +o or you do not have an
enhancement bonus increasing your natural armor bonus."

My questrion is simply does that mean with this feat a Matural Armor bonus of +1 is a +3 for a duergar? And it's per source so an Amulet that grants a +5 would grant a +7, and a cloak that grants a +1 would be a +3 etc? It seems pretty amazing especially considering Nat Armor from multiple sources stack.

[LoneKnave]

I actually don't see why you wouldn't get +2 to all Natural armor enhancers aside from that being stupidly good (well, it's still just AC but you get my point). The way it's worded makes it sound singular (as in each source, not the total armor bonus you get).

[Raisse]

Enhancement bonuses don't stack with each other so if you have an Amulet of Natural Armor +4 and have Barkskin (+5) you would get a total of +7 (+5 from Barkskin, and +2 more from this feat). If your spell wore off you would have +6 (+4 from Amulet, +2 more from this feat).