Using the same setup, I managed to get 3.5km from inside the car on the way home. However, it is way off the tens of kilometers claimed by LoRa.

Line of sight is the answer. Andreas Spiess managed to reach a LoRa gateway 200km away because it was clear line of sight; from one mountain top to another. Here is the height profile of the 3.5km i managed so far:

As soon as I turned East to head home, there was no more LOS.

So there was no way to hear it all the way home (the green pointer):

I should check other options....