Debug Tool - What is the new FOV-Tangent Multiplier?

I just played around with it and found it increases the FOV of the game window on the desktop, which is quite useful for recording/streaming. Try setting both horizontal and to 2.0. 
It takes more GPU power though. I noticed auto resolution kicking in when I tried it in Echo Arena. 

A setting of 3.0 was unplayable. Thats too bad, I was hoping to pin the window with dash and get the "rear view mirror" I've always wanted for that game in my hud ;)

I don´t get it - When I increase the fov in Creed Rise To Glory it works, but it doesn´t on Mage´s Tale or The Vanishing Of Ethan Carter. Is this normal? Maybe it depends on how the game is programmed?