I know how the real armours worked. In a d100 game I created, you can multilayer them just like in reality. My question is this: You are wearing a leather +5 and a chain shirt +1. What is your armour class? +7 or +9?
+5 leather is AC +7, +1 chain shirt is +5, so your AC would be +7. I'd suggest you step up to one of the mediums and reflavor it slightly, instead, however, to actually get a more accurate representation of what that means.
That is not the point. The point is that if we are looking at total AC of a piece of equipment, then a +5 dastana would add +6 AC to a chain shirt, not +1 and the enhancement bonuses of the two overlap. Either we stack the total AC of the equipment or we look at every piece of equipment as though it has two distinct AC values and pick only the highest.
There is no difference with a +5 dastana on top of a chain shirt and a +5 leather on top of a chain shirt (except that the dastana stack and the leather doesn't) in terms of calculating enhancement bonuses. If we look at the leather armour's total AC bonus (+7), then we must also look at the dastana's total AC bonus (+6), before deciding whether they stack with the chain shirt or not. If we look at components, then we'd end up with a +5 chain shirt either way.
It is one or the other. You can't have both.
The difference is that the dastana stacks its AC bonus, but the leather wouldn't. +1 chain with +5 dastana would be +10 armor bonus (4 chain, 6 dastana, enhancement bonuses overlap). Dastana are a weird niche case item, though.
I keep feeling there's something I'm missing in your examples that you are trying to point out.
I think the point he's trying to make is that if the Enhancement bonus to AC and the Armor bonus to AC are considered separate, then someone wearing a +5 leather armor and a +1 chain shirt should count the armor bonus from the chain shirt (higher than the leather armor's) and the enhancement bonus from the leather armor (higher than the chain shirt's).
So in the end, it's really just a roundabout way of asking if Enhancement and Armor bonuses on items are separate or not.
Personally, for some reason I was always under the impression that Enhancement bonuses on armor count as bonuses to the armor's Armor bonus, rather than straight Enhancement bonuses to AC.
That is precisely what I was saying. There are two ways to look at armour when talking about adding it to your AC:
1. The piece of armour is an item. It doesn't matter what that armour is, it is one item. Therefore, a +5 leather gives +7 AC bonus. A +1 chainmail is +6 AC bonus. If this is the case, then, because both are armour bonus to AC, they do not stack, but overlap. Therefore, your armour bonus to AC is +7.
However, if you take the case of the dastana, then a +5 dastana will give you an armour bonus to AC of +6. A +1 chain shirt will give you an armour bonus to AC of +5. The thing is, the dastana stacks with the chain shirt. You would therefore, end up with a total armour bonus to AC of +11.
2. If you look at the fact that base armour bonus and enhancement bonuses on an item is discrete and separate items, then you will get the following scenario: The +5 dastana will have +1 base AC bonus and +5 enhancement bonus. The +1 chain shirt will have a +4 base AC bonus and a +1 enhancement bonus. The dastana's base AC bonus stacks with that of the chain shirt, but their enhancement bonuses will not. Therefore, you will get a total of +10 armour bonus to AC.
BUT, if you then look at the case of the +5 leather and the +1 chainmail, you get the following: +2 base AC bonus and +5 enhancement bonus for the leather, and +5 base AC bonus and +1 enhancement bonus for the chainmail. If they are discrete, then you are looking at a total armour bonus to AC of 10 (+5 base for the chainmail and +5 enhancement from the leather; since they are discrete items, it doesn't matter WHERE the enhancement bonus comes from).
Do you see the contradiction there now, McPoyo?
EDIT: While we are at it, what are good ways of getting Iron Will and Alertness? These two seem to come up again and again in qualifying for PrCs...