3.5 Armor values are pretty weird. I mean, just look at it! Some of them are just plain useless even in P&P; and most are not available in NWN as-is anyways, for example, the differentiation between a +6 Splint and a +6 Banded.
So the Silver Marches Rule Kobolds decided to rework them, and here is what they came up with.
ACP = AC - 2
ASF = AC * 5
ACP = AC
ASF = AC * 10
|Light (incl. Buckler)||1||1||10|
The keen observer will notice that tower shields are now AC4 instead of AC3.
We hope this clears things up a lot, and will make calculating things in your head simpler too. Our resident Drow has been volunteered for sacrificial testing. Happy bashing.