If I move the wires closer together, they still make a 9 volt potential.

If you build something like what I have, be careful with the 9 volt battery.

The gadgets use LEDs, powered by a 9 volt battery, to emit beacons of infrared light that are visible only through night vision equipment.

Suppose you have two wires connected to a 9 volt battery with the free ends of the wires held just 1 centimeter apart.

The electric potential difference between these two ends is 9 volts.

So now I have a 9 meter tall hill (instead of 9 volts).