ArmClamp
I think I said it'd do jack to an aircraft without any tech reason my apologies, just opinion , however my opinion is based on the extraordinary wavelengths of the actual radio signal at vlf freq's.A full wave at 19.8 kilohertz is over 15,000 metres in length if my maths is correct.
Your maths are pretty much on the mark, but there are a couple of other factors that are more relevant.
Firstly, because the VLF stations transmit intelligence they emit sidebands and the resultant harmonics at the power levels we're talking about can still be quite significant.
Secondly, though the electronics are often well shielded along with L/C filters in all the power supplies etc, it is still possible that the enormous power from the VLF transmitters *can* modulate the airframe and any poorly bonded panels *can* behave in a non-linear fashion thus injecting a detected signal into the electronics via the shields or ground returns.
As I've said elsewhere, it's a long shot, (hence the *can*) and hard to buy, but I have seen stranger pheomena with aircraft electrics/electronics.
That makes it pretty hard to rule out.