Turned off 1 monitor in my NVIDIA X Server Settings
X Server Display Configuration > Display Resolution > 'Off' , then 'Apply' (even though 'TwinView' is my Configuration)
Left this setting in settings.json:
"resolutionOverride":"1920x1080",
and just completed the Tutorial!
I was skiddish about changing these settings, since in the past NVIDIA's settings applet required write out to the Xorg.conf file, restart, sudo access, and a sacrifice to the gods to get configured correctly. Like all things, it has gotten better with time!
Thanks for your help & replies! off to play!