My confusion here is hilarious.
If like me someone has mostly used the Potentiometer with a micro-controller, they might start to always think of pots as voltage dividers since that’s the config you need for analogue pins.
Above, I’m confused because I’m expecting the second configuration pictured in my original post vary to the voltage coming out of the right most pins. That’s wrong; it wouldn’t (much) impact the voltage of the data terminal but it would vary the resistance.
I think I have made pots in the rheostat config before when I’ve been following circuits from “The Art of Electronics” by Horowitz and Hill. AOE mostly uses schematics, so I have never, until I saw that youtube video today, seen someone just solder slider to one terminal before.
Now I know 
Thanks again Bob.
