With the new material out, there is still some learning how the rules work with Warforged. I am asking about a Warforged Sorcerer and how Mage Armor affects him. 

I will be using a 1st level character and a 5th level character for my examples.

We know how Mage Armor works. Base AC =13, Dex bonus = +3 (I have a 16 Dex.) A normal human would have an AC of 16.

This is how I envision the Warforged. Base AC = 13, Dex bonus = +3, Integrated Protection = +1. AC = 17 Sorcerers are not proficient in light armor starting off.

5th level

Feat = Lightly Armored for both characters, Point from feat added to STR. so it is irrelevant. 

Human w/Mage Armor = AC = 13, Dex = +3 Still has AC of 16, 21 w/shield

Warforged = AC = 13, Dex = +3, Integrated Protection +4. AC = 20, 25 w/shield.

So one of the questions about Integrated Protection is, is it armor? I think the answer to that is as long as it's the Darkwood version of the integrated protection. In the chart specifically for that feature, it has (Armor) and (Unarmored) listed next to the apprpriate armor bonus. If you are wearing Full Plate and cast mage armor, it does not stack, the same is true with the Heavy Plating feature of the Integrated Protection option, where as if you are are using the Darkwood option, it is the equivalent a hard leather outfit. There for, your base AC can still be 13, and you still gain full benefit of the integrated protection feature. This also does make sense for the canon of the WarForged, they are walking tanks, they are made for war, they should be harder to kill in battle by their very nature.

Am I off base here? Comments? Do I have it right on the nose?

So to be clear your saying that it's either 11+dex+proficiency bonus or 13+dex?

would you use proficiency bonus w/mage armor? If not, why?

Quote from Akito >>

So to be clear your saying that it's either 11+dex+proficiency bonus or 13+dex?

would you use proficiency bonus w/mage armor? If not, why?

 1st question is yes, you get to pick.

2nd question, you would not use your proficiency bonus with mage armor simply because it doesn't tell you to do so.  If you want to calculate your AC using mage armor, you get 13 + dex.  If you want to calculate your AC using Integrated Protection, it's 11+dex+proficiency.

Yes, this means that, in the long run, you will likely not be casting mage armor as a warforged.

Minor note, but pure Wizards or Sorcerers - characters without Light Armor Proficiency - would still gain a benefit from casting Mage Armor, as the +Proficiency to armor class that comes with the Warforged's Integrated Armor only applies to characters with Light Armor Proficiency.

Any Warforged *with* Light Armor Proficiency gains no real benefit from casting Mage Armor.

While I understand that you must choose only one calculation method for your ac, can you clarify whether "Integrated Protection" is in fact an alternate calculation method.

The specific language for this according to dndbeyond is  "You gain a +1 bonus to Armor Class." Similar to bladesong's : "You gain a bonus to your AC equal to your Intelligence modifier (minimum of +1).", and in contrast with mage armour's "The target's base AC becomes 13 + its Dexterity modifier"

Jeremy Crawford confirmed via twitter in 2016 that the bonus to ac from bladesong does stack because "A bonus stacks with anything except another bonus from the same source" (which i assume refers to something along the lines of two different paladins casting shield of faith on the same target, although i think the specific meaning of 'from the same source is irrelevant in this specific case')

Since the language for Integrated Protection indicates it to be a bonus rather than a calculation, and mage armor is not only not a bonus, rather a calculation method, and is also from a different source, should the two not stack?

TLDR: is warforged ac bonus not a bonus rather than an alternate calculation method?

ah, awesome, thanks, hadn't realised it had changed