Here's my experience... Both Muroi and Neese spawn on the rocks in the center. Sometimes a normal mireguard spawns on the tallest rock and neither Muroi nor Neese appear. That is most common. Once in awhile Muroi will spawn on the tall rock along with 3 mireguards on and near the rocks. When Neese finally appeared she was on the lower rock, Muroi also appeared at the same time on the higher rock along with 2 mireguards.
At level 50 I filled 3 packs full of salvage and loot before Neese finally appeared. Muroi appeared maybe 6 or more times during the 6-8 hours. It is hard to imagine the bracer is really worth this kind of effort.