Game root/system
"Main Postal Game name.ini"
Example Postal2.ini
FullscreenViewportX=****
FullscreenViewportY=****
User.ini
DesiredFOV=85.000000
DefaultFOV=85.000000
For 16:10 I use the FOVCalc with the value 85 and get 95.4370607151, my new FOV values.
1600x1200
1920x1200 FOV 85
1920x1200 FOV 95.4370607151
Hor +.
Layman def.
Vert - games get that way because the game engine is using the same Hor distance for screen displays. Because the widescreen resolution is wider the game zooms in to return to that point. This is where you lose Vert viewing area.
By increasing the FOV we return the game to the original zoom level. This removes any Vert loss. However, since we have a wider resolution we also get Hor +.