I would have to agree that its mostly random. I have found some of my best items (Stormsheild, Shaeffers) with my 48% MF Pally and spent literally hours with my Zon using anywhere between 110 -600 MF on Pindle runs without seeing a single unique, then out of boredom I divert to Eldritch and he drops an Eaglehorn on me lol.
Hey its my first post!!