@ChartreuseK Interestingly, adding the DitherPPI setting for GhostScript says
"forces all devices to be considered high-resolution, and forces use of a halftone screen or screens with lpi lines per inch, disregarding the actual device resolution. Reasonable values for lpi are N/5 to N/20, where N is the resolution in dots per inch."
I tried several DitherPPI settings without any change.