You can set custom settings via file editing. For that, you need to edit two files in XIII\System -> XIII.ini & DefUser.ini. Resolution -> XIII.ini
Search for FullscreenViewportX=
and set them accordingly. Field of View -> DefUser.ini
Search for DesiredFOV=
and set the same value for both parameters. Attention: The DefUser.ini is loaded only once by creating a new profile!
Please let me know if 4K does work on XIII.
For alternative resolution/FOV combinations you can find information on: https://pcgamingwiki.com/wiki/XIII#Widescreen_resolution