So far, someone already managed to make out how to fix it in general for 21:9 and other common resolutions (post #5 in this Steam forums thread) through changing one HEX value in the executable.
Now I am stuck since I don't know how to calculate the right HEX value for my resolution of 3360x1050.
Thanks for help!
/so far I tried the way described on the "common hex values" page http://www.wsgf.org/article/common-hex-values
divivded 3360 by 1050, getting 3.2
used this calculator to get to the hexadecimal of 0x404ccccd
The issue was with the correct order, disregarded the reverse order for the HEX entry. Now I got the aspect ratio working properly, sadly though the scaling of the game and the second players HUD is still messed up:
/last edit
Turned out that EDF had some issue with proper managing the switching between single monitor and dual monitor splitscreen. So after another restart without changing the resolution in between it now works as intended



