I'm currently using 16:10 monitor (1920x1200)
And there's no support for 16:10 monitor. (which means you can't remove black bars top and bottom)
Far Cry 3 and 5 officially supports 16:10 ratio.
Tried editing the GamerProfile.xml file at Documents/My Games/Far Cry 4/{YOUR_UPLAY_ID}? May be possible to set the resolution there, could be you need to make the file readonly after saving your modifications.