Those size factors are helpful, thank you.
Now in regards to the shield spell, if a Thrassian were built with arcane value allowing it to cast shield on itself, would the spell AC add to the Thrassian's natural AC or replace it? In the same respect, if a shaman were to research a divine copy of shield and cast it before shifting to his or her totem form, would it add to the animal's natural AC or replace it if the spell is higher. I would assume the highest value wins and the two values wouldn't stack, but there has been dispute among the players as it isn't explicitly stated either way.