[Armor Penalty & Arcane Spell Failure %]

[Quandary]

Shouldn't Arcane Failure be based on the Armor/Encumbrance Penalty instead of the generic Armor Type?

If your Armor Penalty is lower (from MW armor, from a Trait, Armor Training, Feat?),
why is the Arcane Failure Chance (for Somatic Spells) the same,
even though physical skill checks (SOMATIC MOVEMENTS) are only penalized by your actual encumbrance penalty?

Basing Arcane Failure on Encumbrance Penalty is more consistent and removes the ridiculous situation of a caster who has an Arcane Failure Chance if they wear studded leather, but not if they're carrying a giant anvil on their back, as long as they're just wearing robes.

This could be based off a simple, explicit formula like 5% ASF/ -1 Encumbrance Penalty.
While we're at it, why not convert ASF% to d20, since it seems to always be in 5% multiples anyways?
And this goes over into Combat a bit, but conditions like Prone, Grappled, etc, could increase ASF%...???

[Krome]

because an anvil on my back does not restrict the fine motor motions of my hands when casting a spell.

On the other hand, soft leather gloves are less restrictive than full metal gauntlets.

I think the arcane spell failure should be a function of the type of armor worn. Encumbrance in general has nothing at all to do with those movements.

[Quandary]

I don't believe Studded Leather comes with gauntlets by default (and AC isn't effected whether or not you wear them)
Wielding a Shield increases the ASF%, even though you can cast a spell wielding any 1H Weapon in the other hand with NO ASF%.
Likewise, what about the "Armored Kilt" type of Armor Kit which would not seem to effect the upper body at all (yet have ASF%)?

This just seems a more elegant solution (to me).
Unifying ASF% and d20 could probably negate the need for a separate ASF% column completely, and just adds half a sentence to the effects of Encumbrance. It seems like Pathfinder is TRYING to "iron out" some of the COMPLETELY pointless sub-systems of D&D, and this seems like it might qualify. I understand the argument that somehow magical movements are more delicate than non-magical Skills, but I think the gains from simplification out-weigh the benefits of having this micro-sub-system. (with no other game usages I know of)

Anyhow, that's my 2cents. :-)

[Pathfinder X]

I say it should be based upon straight Armor Check penatlies, change it to a d20 roll.

layering armor (ex.An armored Kilt) should add an additional -1 Armor check penalty.

Spellcasting is based upon not just the hands moving but intricate movements of the entire body.