Stacking of Peltier units - Part 3

In this video I repeated the experiment of part 2 with some extra steps. I was wondering if I could somehow squeeze out more from the system. I could go down 5°C deeper, but that's all. Unfortunately, I cannot remove more heat with this particular cooling system, so the cooling power of the bottom Peltier cannot be further increased. This hinders the additional decrease of the temperature on the cold side of the top unit. Still, -45°C is pretty satisfying for me, I could go deeper than I ever could go.