The idea of absorption does not work with this kind of shield. It's levels are static. It's protection isn't supposed to increase as it takes more damage. Just the opposite in some ways. Since the more it gets hit, the less power it has to absorb future hits. It's charge decreases until it runs out of power and the shield goes down.
As far as the OAF thing, they should all be OIF except the "dueling" shield, which should be IIF. The shields have all been displayed as some kind of belt or backpack. If you knew what a shield generator looks like then it would be pretty obvious. But, since it's strapped to the person wearing it, it should be an OIF instead of a OAF. The dueling also, were described as being well hidden. It would just as likely be hidden in a ornate ring, or wrist watch, as it was to be a brooch of some kind. It could be anything you were wearing. Which in my opinion makes it IIF.