Psybermagi says:
The book I have says 4 but in another game I play the DM said 5.
Every official source I have seen put the Goblin (which is the base of your Duende) at 4 HP. This include the sci-fi version of the Goblin (forgot what it's called). So the 5 for the other GM is a house rule. Which is cool and makes sense for the reason you stated.
Back on armor, for the base traits, you have:
- Tough: get +2 HP.
- Armor: get 3 ablative HP.
- Diehard: drop to 0, then bounce back to 2 once per day.
- You can spend 6 XP to gain 1 HP.
And, having asked earlier, the armor proficiencies are gained like weapon proficiencies. So they are a little cheaper than a full trait.