benger,
To start with, wondering how you have things set up:
In FWS, do you have "Enable Detection Override" checkmarked & details filled out? It's under FWS menu, Settings, Configuration, Display Detection.
If you are not using the above FWS override, that is the first thing you should do. Here are the FWS settings most likely to work.
Width: 2560
Height: 1080
Hud Width: 1920 (16:9 fake center)
Hud Height: 1080 (16:9 fake center)
Horizontal Display Count: 3 (with fake sides)
Vertical Display Count: 1
Hud X: 320 (which is 2560 minus 1920, divided by 2 = width of fake side)
Hud Y: 0
(These entries are for your 2560x1080. But we are pretending you have PLP or it likely won't work (ie fake 16:9 center, fake skinny sides). This likely gives full spread with proper 16:9 HUD size etc.)
Let me know your result.