Small transfomer not being cooled by conduction panel.

Hmm, I think i might be wrong, it's probably just the performance of the conduction panel, because temperature doesn't rise either.

Metal ores are generally pretty low on the thermal conductivity level, so the thermal transfer to the conduction panel will require the temperature difference to be much higher to reach equilibrium. However, large transformers are made from refined metal, which all generally have much higher thermal conductivity, resulting in more heat transfer with a smaller temperature difference.

Using steel for the small transformers will likely significantly improve the thermal transfer, or swapping the metal ore used for one with a higher thermal conductivity (although the only metal ores that're decent at it are aluminium ore or wolframite)