My experience is limited to certain routes, but it's always far too warm for me on the overnight flights from SEA, YVR, and SFO! Sweltering.

I want to sleep on my flat bed, not toss and turn in misery. It rather defeats the purpose to provide a spot to sleep and then make sleep inpossible because of the heat.

I do ask politely if the heat could be turned down, yet it never seems to get cool.