Does Armor Expert work for shields? (i would assume no)
Can Comfort enchantment be applied to shields? (i would assume no)
What are other ways of reducing shield's ACP other than masterwork and mithril?
Darkwood also lowers shield's ACP by 2. I think all towershields are metal, so darkwood doesn't apply here, but a darkwood heavy wooden shield has ACP of 0. If you use it without being proficient, you'll take a penalty of 0 to all physical skills and ability check.