They can be square.
Also, I think it's dumb that Full Plate offers 0 protection from spells. Sure, Lightning Bolt will go straight through, depending on material, but a Fireball's effects will be severely dampened, and anything to do with draining life force should really have to make contact with skin...also, kinda silly that if a ray of frost hits my shield, it does as much damage as if the same ray hitting the barbarian in arm. >.> Just sayin'. Speaking of which, even as much as Ray of Frost hitting Chain Shirt vs. Scale Mail. Though part of this comes from me thinking armor should give small amounts of DR, too(different amounts against different things, depending on armor of course; Chainmail might have DR 4/bludgeoning or piercing, DR 1/slashing, and Energy Resistance 2 to cold, and 1 to acid and fire, while Cloth might have DR 1/slashing or piercing and Energy Resistance 4 to cold, 1 to acid and lightning, and then again on the other end of the spectrum, Full Plate might have DR 6/bludgeoning or piercing, DR 3/slashing or piercing, and DR 2/bludgeoning or slashing, with ER 7 to cold, 4 to fire and acid, and 1 to sonic.
Of course, that's probably wildly unbalanced, but AC bonuses would probably be lowered, fairly significantly. Shields might have their AC bonus boosted to 'compensate'. Still think shield bonus to AC should be part of touch, though.
Note that I expect none of this. Just me ranting.