When you fail a smelt, you get a pile of a smaller size. That part is good, but, if you have a pile in your backpack of that size, it doesn't add it to that pile. Instead, it'll spawn another pile of that same type. So, if you fail a bunch of times, then your backpack will be cluttered with all of these smaller ore piles randomly placed in the backpack. I don't believe that this is correct, and, even if it is correct as per the era, that it should be this way considering the aggravating nature of having one's backpack entirely filled.
They can, but the point he's making is that if the failed smelt process drops the remains to your pack, any matching types should auto-stack. Seems worthy of a bug report. Annoying but definitely not game breaking.
Workaround: Add to your macro.. Double click the small ore type, target another small ore type, double click that new ore type, target forge. It will combine your smalls into the next type and then that type will be big enough to attempt to smelt
There's a couple more reasons to follow LanDarr's advice, those being weight and efficiency. Taken from the stratics mining guide Let's start with weight: Large Ore: 12 stones, 2 ingots, 6 stones per ingot Medium Ore (both types): 7 stones, 1 ingot, 7 stones per ingot Small Ore: 2 stones, 0.5 ingot, 4 stones per ingot If you pack your horses/backpack with nothing but small ore you'll get far more ingots per haul Next, efficiency on failures Large Ore -> Medium Ore 1 ingot lost Medium Ore -> Small Ore 0.5 ingot lost 2x Small Ore -> Small Ore 0.5 ingot lost So if you're always smelting 1x medium ore, or 2x small ore at a time you minimize your potential losses.
