Btw, upon rewatching the Stade 2 doc, something I hadn't noticed before, and something Tom de Engine and Nicko conveniently ignored, is that the heat signal is not just stronger in the rear hub,
but also in the lower part of the left seatstay, whereas there's nothing heated in the other seatstay.
They show the heatsignal very clearly in the documentary starting
at ca. 9:00.
Now, that heat signal is fully compatible with what you'd expect of a rear hub motor which, after all, needs a battery, which, in turn, you want to be located close to the motor, i.e. in the lower part of one of the two seatstays.
This is illustrated very nicely
at ca. 9:55 in the documentary.
Link to the documentary once more:
https://www.youtube.com/watch?v=15kIyBhsX8o