Measuring >40VAC from 230VAC Phase against air
No, this is not reflection. Reflection only comes into play what the length of the wires are in the order of the wavelength of the AC frequency.

For 50 Hz that's \$\lambda\$ = \$c/f\$ = 3E8 m/s / 50 Hz = 6000 km.
I'm guessing your wires aren't that long.

What is happening here is that you made a capacitor. Two conductors side-by-side have capacitance to each other. That will be a low value capacitance (less than 1 nF would be my guess) but enough to develop a voltage across your DMM as your DMM has a high input impedance. Usually that input impedance will be 10 M ohm.

As soon as you apply a load to that conductor, the voltage will drop as the capacitance has a high impedance. You cannot extract much power from it. The power is enough to show a reading on a DMM or make a neon-lamp voltage checker screwdriver light up (faintly) but that's it. Even if you touch it you might not even notice the AC current that is flowing as it will be small.