This came to mind reviewing the last couple posts about cooling the motor and another mentioning cooling the battery. I've often thought that anything over 2S, maybe 3S is just inviting the cells in the middle to overheat.
Has anybody tried opening up the battery pack and adding some spacers, say 3/32 balsa, between the cells to allow at least some air circulation around the inner cells? It might even be useful to duct the cooling air into one side of the battery and force it through the gaps between cells to an exit. Hot air from both the motor and the battery could be ducted out the back, at least of the cowl, for a bit of thrust.
Look at full size planes. The cooling air is best brought in from the high pressure in front of the motor into a plenum that allows it to slow down so it can flow between cooling fins.
The Rare Bear and the Cessna 172 are good examples. On the Bear high pressure air(400mph+) enters the cowl through a gap around the spinner into a large chamber in front of the cylinders. Similar on the 172, but the chamber is on top. On both planes the air slows, expands, cools, and then flows through the cooling fins fairly evenly and at a much high Reynolds number.
Cheers I might actually build another electric plane this year.