What are the overall dimensions of the part/blank envelope? This along with the needle count determines the resolution.
A new place, where you can update Default settings:
File -> Utilities -> Customer Defaults -> Gateway -> Facet Settings
Tune up common facet settings there.
And now values of parameters at File -> Utilities -> Customer Defaults -> Manufacturing -> Simulation & Visualization -> IPW:
IPW Tolerances: Tolerance Mode = Needle Count
Needle Count: Coarse = 2000 Medium = 3000 Fine = 4000
Saved IPW Resolution = Fine
Displayed IPW Resolution = Fine
Animation Accuracy = Fine
Some time ago I was working as a NC-programmer in a workshop.
I used this values to get excellent display picture.
More over I advise you don't forget, that NX is rather economical app. I mean it doesn't use all RAM memory or CPU/VGA, if you don't ask it. So you probably can increase a resolution this way: View -> Operation -> Regenerate Work. Also you can check your current facet settings here: View -> Operation -> Facet Settings.
Dont forget - you must to pay for good IPW resolution. Currency - time of simulation, when you wait-wait-wait even after set checkbox "Show 3D material" ........