Eddis, Attolia, Sounis

Along with the second question, I think the Magus also plays a big part in Sophos' decision. In TT the Magus makes it clear to Gen and Sophos (I can't remember if Ambiades is still hanging around at that point) that having the Medes on their land is BAD. In addition to hero-worshiping Gen, Sophos also greatly admires the Magus, which of course would affect his decisions. So, between the pressure of his well-meaning neighbors and his favorite adviser, he kind of had no choice, despite being king.