Whomever Smelt it, Dealt it

Yeah, I know. . . the title has very little to do with this question, I just thought it was funny.
Anyway, I'm reading the wiki and have been trying to figure out this whole % thing with the ore. I did successfully create a bar of iron on my first go round but was left with 5-6 dross.
The wiki says any ore that couldn't be melted into another bar, or a bar, will be put towards the next smelting. . . but it also says ore that couldn't be turned into a bar will be left as dross.
So which is it? It turns to dross or it goes towards another bar? How do I minimize dross leftovers, aside from using 20 ore and 3 lime?

Anyway, I'm reading the wiki and have been trying to figure out this whole % thing with the ore. I did successfully create a bar of iron on my first go round but was left with 5-6 dross.
The wiki says any ore that couldn't be melted into another bar, or a bar, will be put towards the next smelting. . . but it also says ore that couldn't be turned into a bar will be left as dross.
So which is it? It turns to dross or it goes towards another bar? How do I minimize dross leftovers, aside from using 20 ore and 3 lime?