If you allowed this, I would consider it as Robes, AT 2 and 1 step Crit reduction vs Piercing.
That might be too powerful.
The Cyberpunk2020 game had similar tropes. Everything was Kevlar this and Kevlar that..
Doesn't matter if you have a Kevlar bandanna or t-shirt, you're still getting stuck, but the projectile is now covered with cloth, in your body.
I'm not saying that the Khan's armor was anything like that silliness. But for encumbrance I'd say Robes. Hey.. maybe that's why Mages wear robes. If they're made of silk and can reduce arrow crits....
I kinda like the image of a mage in robes. Maybe now, I have a reason. It isn't necessary, just a dress code around the Guild; other people don't realize that it's actually armor.
Thanks!