I have only seen him up once. He was in a small side tunnel at around neg 80, neg 500.
It was late, I was tired, and I didn't know the zone so well, so I didn't pull him. He sees through invis btw. He is the first spawn in the side tunnel, just at/past the corner. There are two more spawns just past him at the end of the tunnel.
I have since discovered that there is a safe area to pull to nearby - the small side tunnel on the opposite side of the main tunnel (around neg 110, neg 450), a little south from where the kobold spawns. There is one spawn at the end of the this tunnel which you can clear first, or just ignore (aggro range is tiny). There is also one wandering bruiser which you can kill or avoid.