With your guide error RMS at around 0.23 px, settling at < 1.0 px sounds reasonable. You should open your PHD2 Guide Log in PHD2 Log Viewer and take a look at what is happening during settling (settling will be highlighted by the app). For example, is Dec oscillating? That should give you a pretty good idea about what is happening. If you would like help interpreting what you see, feel free to post your PHD2 Guide log in the PHD2 forum.
Andy