If the molds take 1 unit and you’re adding a nugget at a time then you will never accumulate enough iron to fill the mold because it gets converted to steel before you can get enough to fill it.
The reason I don’t want to think about the heat is just that it’s slightly less straightforward to figure out the optimal temperature threshold in terms of KU waste. With repeaters it’s easy to match up with the known time to make steel.
Btw I made a video but it won’t let me attach or link to it, how do other people post things?