The effective crafting speed inversely scales with the loss and it is not linear. You can change all those times in mod settings.
But that is why possible loss is made possible for those who want it, if you allow for 10% of the ingredients to be lost you smelt much faster than only 10%. You need more iron ore but you get more iron plates in the same time.
Default setting for lossless was same as vanilla smelting time from what i recall, you need exact same amount of furnaces to make a full belt. Oh, it also probably reads the default time from data so if other mod changes that first then the defaults are different.