I am not sure of the whole LPI settings thing...
Therein lies your problem. What you need to do is to get sure of them.
If you're working with vectors, forget the Gerbertone and switch to Classic Dot which gives you LPI setting control. LPI controls the size of the dots and works like this:
The smaller the dot the less you are aware of the dots but the less "tonal quality" you will have. When you reduce tonal quality, things are more like solids and you also see more banding.
The larger the LPI number, the smaller the dots. So if you are getting banding, lower the LPI setting until you have an acceptable compromise. A good middle setting for Classic Dot is an LPI of 53.
If you are working with a bitmap then use the STC Photo halftone and try the same 53 for the LPI.