It bothers me that the smelter uses coal based on the amount of time it's running, not on the amount of ore it processes. Like, 20 coal + 10 ore should equal 10 bars, but it doesn't because the amount of coal used is 1 coal every ~15 seconds and it takes ~31 seconds to produce a bar.
I should be able to load up the ore and coal, walk away, and come back to 10 bars, with both the ore and coal hoppers being empty. Instead, I always end up with 1 or 2 left over in either after the other has run out. It's frustrating.
I get that it's more realistic that the smelter uses fuel at a certain rate, but it doesn't make sense to say that, because the smelter isn't running constantly and using coal the whole time; it only runs if it has both coal and ore in the hoppers. If the smelter were constantly running and using a set rate of coal, regardless of if there is ore to process, I'd get it. But since it only runs with both, it should use a set ratio of both, not based on time running.