I asked something very similar to this in
another thread.
There it was said that cooling a TEC with anything less than watercooling would be a completly useless waste of enargy. BUT in the past though less powerful TEC were used with a HSF arrangement... and that was cooling a CPU die. so it stands to reason that a small low power TEC could be cooled by large heatsink alone.
Of course I don;t have anythig resenbling a TEC... but maybe you can test running the pelt on lower voltages I have a feeling there in lies the key.
~ Boli