Mixing Armor in Pathfinder

[Zubrowka74]

The PF SRD indicates that the four-mirror armor (ac +6) can be worn over chaimail (ac +6) and in fact it is often so. I do not own UC so I can't check but how can a chainmail plus four pieces of steel be way more protection (+12) than any plate-style armor ? I'm pretty certain I'm reading this wrong or that the SRD doesn't give the full story. Even with the variant piecemeal armor rule this doesn't add up (+10).

[Agent 451]

In UC the four-mirror armor torso piece (piecemeal armor variant has armor split into arm, leg and torso pieces to form a total armor suit) is +5 ac. If you combine with chainmail you get a total of +6 ac, 5 from the four mirror torso, and +1 from chainmail arm pieces. Chainmail leg pieces grant no extra ac, and there are no four-mirror armor leg pieces. Now, if you are wearing a leg, torso and arm armor pieces you get an extra +1 ac for having a complete suit (doesn't matter what that they are from different styles of armor).

A non-piecemeal suit of four-mirror is +6 ac, whereas a piecemeal armor with four-mirror torso and chainmail leg and arm pieces would be +7ac...I think.

edit: The piecemeal armor rules are also up on the pfsrd.

[Zubrowka74]

Yeah, that would make more sens but they seem to imply that you can add the four mirror (torso) to a chaimail torso. This is basicaly some kind of platemail. It's the numbers that don't make sens.

[Drelua]

I'm pretty sure the bit where it says there's chainmail under it is just describing the armor, not saying you combine the two types of armor. It's just like how Full Plate is described as being worn over a thick layer padding. This doesn't mean you get to add the bonuses from Full Plate and Padded together, it's just telling you how the armor looks.

Besides, even if you did wear two types of armor at once, armor bonuses don't stack. Armor check penalties might, though.

[Yora]

The description is weird:

This armor consists of four plates harnessed together with leather shoulder straps. Two round plates protect your front and back, while two smaller rectangular plates cover the sides of the torso. Four-mirror armor is worn over chainmail to provide added protection, and comes with a spiked helmet with a chainmail hood.

But it doesn't actually provide any additional protection at all.
And its price is much cheaper than chainmail, while it has entirely identical stats. It's just 5 pounds heavier.