The Arachosians and Kissians were both tribes, located near or in Afghanistan/Iran.To me these look pretty much the same. Both have a cap/headband on their heads and long sleeved shirts, and high boots. As for their usage in my armies, they are both part of the Persian Army that i plan to field.
Here first is a look at the Kissians.
Here are a few close-up of the pose that makes up the two units of Kissians.
Next up is the unit of Arachosians.
Here is a close-up of one of the figures, chosen at random. (I could have chosen a better painted one i think).