xAlex79, I have an idea. Since the game takes the Aspect Ratio from your main desktop resolution to make the FOV, you could make a custom resolution that's the same AR as all 3 of your monitors.
4360x1440 is your playing res, so that like 3 something as an AR. So lemme do a conversion to a smaller X value to actually fit within the limits of the main monitor.
4360
2560 X
1440
0846 Y
So you need to make a Custom Res of 2560x846. It's roughly the same AR.
Use
this Guide to make the custom res. You can also try
this Tool which will do most of the manual work for you.
Now after you have your resolution, run change the desktop to it. Launch the Game with you current SoftTH settings so the game should launch in 4360x1440.
You should now have a non-stretched FOV. Try it out.