Smelting batch sizes was rejecting the task completely if the required amount (based off the batch size multiplier) wasn't sufficient in inventory. It now does a "best efforts" approach to smelting where it tries to smelt as close to the batch size multiplier as possible.
If batch size is set to 8 ... it will attempt to smelt 16 ore for 8 bars ...
If there is not enough ore, then it will try 14 ore for 7 bars ...
If there is not enough ore, then it will try 12 ore for 6 bars ...
And so on...
1.0.10 · Space War Economy Idle patch notes · SteamPeaks