XCOM: Enemy Unknown

Default FOV is mostly Hor+, sometimes Vert- in Strategic mode (HQ).
It is not recommended to alter the FOV of Tactical mode (missions): the resulting slightly misaligned UI would hurt the gameplay quite a bit.

The mouse position is off the further it gets from the center of the screen. This results in being forced to position the mouse in strange areas trying to get the game to see you want to click on the square 4 spaces away.

Launch the game once to generate all config files, then navigate to %USERPROFILE%\Documents\My Games\XCOM - Enemy Unknown\XComGame\Config\

1. XComCamera.ini

[Engine.Camera]
DefaultAspectRatio=1.778
bConstrainAspectRatio=True
ConstrainedAspectRatio=5.333 //your desired width by height ratio

2. XComInput.ini

Under [Engine.PlayerInput] ADD the following lines:
Bindings=(Name="T",Command="FOV 140")
Bindings=(Name="B",Command="FOV 110")

Under [XComGame.XComTacticalInput] FIND the following line:
Bindings=(Name="T", Command="T_Key_Press | onrelease T_Key_Release", bPrimaryBinding=True)
...and replace it with:
Bindings=(Name="T", Command="FOV 130 | T_Key_Press | onrelease T_Key_Release", bPrimaryBinding=True)

Save changes then run the game.
Press T to fix the FOV.

• In strategic mode (HQ), some rooms/menus require a slightly lower FOV. Press B instead.
• In tactical mode (mission), pressing T once during the landing cut-scene will fix the entire mission.

130 is a good value for bezel-compensated 48:9, and works for lower TripleWide aspects too.
110 works better for classic 15:4 TripleHead.

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The mouse position is off the further it gets from the center of the screen. This results in being forced to position the mouse in strange areas trying to get the game to see you want to click on the square 4 spaces away.

(HQ) Some misaligned menu items. Manual aiming/dodging is impossible during UFO interception.
(Mission) Mouse cursor's course is distorted. Take it slow !
(Mission) Cosmetic glitches: highlights and status bars do not match actual objects.