[Tigerious]

I found a workaround. After browsing many forums about dual screen and games with full screen mode it ended to use Regnum Online Client on one screen without window decorations, this can easily be set on KDE.

In case of some interested people here is the video and screen setting from "xorg.conf" :

Section "ServerLayout"
    Identifier     "X.org Configured"
    Screen      0  "Screen0" RightOf "Screen1"
    Screen      1  "Screen0" 0 0
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"
    #Option         "Xinerama" "0"
EndSection

Section "Monitor"
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "Samsung SyncMaster"
    HorizSync       30.0 - 75.0
    VertRefresh     56.0 - 61.0
    Option         "DPMS"
EndSection

Section "Monitor"
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "Samsung S23B350"
    HorizSync       30.0 - 81.0
    VertRefresh     56.0 - 75.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 560"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 560"
EndSection

Section "Screen"
    Identifier     "Screen1"
    Device         "Device1"
    Monitor        "Monitor1"
    DefaultDepth    24
    Option         "RenderAccel" "true"
    Option         "AllowGLXWithComposite" "true"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "RenderAccel" "true"
    Option         "AllowGLXWithComposite" "true"
    Option         "TwinView" "1"
    Option         "TwinViewXineramaInfoOrder" "DFP-0"
    Option         "metamodes" "CRT: 1920x1080 +0+0, DFP: 1920x1080 +1920+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

This mostly result from "nvidia-settings" tool and can be adjusted for custom settings.