As i was pleasured last night, today i got the behaviour that Xorg-server doubled the viewport of LVDS1 (laptop screen) --same-as VGA1 (external monitor): scratch! - external Monitor spots the RecalBox menu and Kodi only in a 1280X800 view upper left inside a 1920x1080 view.

By your help i fond the xinitrc and wrote:
# xrandr --output output_name --off
DISPLAY=:0
xrandr --listmonitors | grep VGA1 && {
xrandr --output LVDS1 --off
xrandr --output VGA1 --mode 1920x1080
}

out of that.