I think in the later game (iron + steel age), processing larger amounts of copper should be easier and more satisfying. My suggestion would be a large crucible that can be filled with copper nuggets and heated on a forge.
In the later game, copper is still useful and can be used to make lanterns. However, while building a huge cementation furnace to create steel, smelting copper with a crucible in a campfire feels very unsatisfying to me and is very inefficient. While this doesn't matter for processing small amounts of copper, for large quantities (6 ingots), the heating process is very slow and the temperature dynamics between the campfire and the crucible feel very unintuitive as the copper has to stay at high temperature for a pretty long time and all melting progress is near instantly lost the second the copper drops below its melting point.
My suggestion to make copper processing in the later game more attractive would be a large crucible that can be heated in the forge. The forge is well established in the later game and its way of heating metal feels much more intuitive. The large crucible can obviously hold more ingots than its smaller version (maybe 12 or 16). In addition it would be very nice if it were possible to cast copper plates in later game using the large crucible.
I might have missed some important information and the campfire heating system is actually super easy and the things I say I feel are obviously subjective. However, I wanted to suggest this for a longer time and wrote this after wasting a lot of charcoal only for the copper to instantly solidify after dropping to 1060° for 5 seconds.