Issue description:
As 16 Iron bars = 6 Iron Ingots (144mb), smelting this should be 864 mb total and so one single bar is equivalent of
864 / 16 = 54 mb.
But it gives only 48mb
It was correct in 1.12.2 with 8 iron bars smelting exactly to 3 ingots, so I see this as bug

If crashed, link to crash report (use a site such as pastebin):

Versions:

• Mantle: 1.6.109
• Tinkers Construct: 3.0.4.197

Confirm below that this issue is not covered on the roadmap or "Whats New?"

Can it be reproduced with just Tinkers Construct? If not, list the other mods required to reproduce the issue.

Should be fewer than 10 mods, you should be running no mods besides those 10 when you reproduce the issue.

Intentional. Smelting bars is less efficient, but you can also cast them for that amount.

Ok. Can I fix it with custom datapack if I prefer old ratio?

Yes.