Agree 100%! We tweaked the simulation numbers a bit in the background, but we couldn't fix the exact issue you mentioned. With more time, we could have balanced it the way the player expects it to and show more clearly the impact the player has.
Simulation Explain: It propagates heat from the heat source to tiles arround it. Insulation prevented heat from spreading to the next tiles (with some resistence values). But in the Simulation our insulation absorbed too much heat- trapping it there. But we wanted more like a effect where the player could direct the "flow" of the heat.