Which Xorg snippet did you try? Specifically, did you try the following?
Proprietary NVIDIA driver
DPI can be set manually if you only plan to use one resolution (DPI calculator):
Section "Monitor" Identifier "Monitor0" Option "DPI" "96 x 96" EndSection
You can manually set the DPI adding the options below on /etc/X11/xorg.conf.d/20-nvidia.conf (inside Device section):
Option "UseEdidDpi" "False" Option "DPI" "96 x 96"