pyrotech-1.12.2-1.3.13
Currently the bloomery/witherforge can process 1 and 3 blocks respectively, but they only use a single block of fuel per run regardless of amount of ore blocks inserted. IMO the required fuel block count should depend on the amount of ore.
Also, the bloomery/witherforge both accepts 16 blocks of fuel blocks, one could make a silly mistake by rightclicking it with a whole stack of fuel, and additional fuel does not provide any benefits...
So I'd suggest to make the fuel slot size depend on the amount of ore block inserted. For example, if you have only 1 block of ore in you wither forge, you can only insert 1 fuel block; And if you have 3 blocks of ore, the forge cannot be ignited unless you have inserted 3 fuel blocks.

Allright, apparently I didn't read the manual properly.
But from a user's perspective this effect is not quiet obvious: although slowly, 3 blocks of ore can be smelted with a single piece of charcoal. There should be a minimal requirement for fuel value per ore (below this the bloomery cannot be lit) like the TFC 1 ore 1 charcoal balance.

[...] but they only use a single block of fuel per run regardless of amount of ore blocks inserted.

They consume all the fuel inserted. Fuel is anything with a burn value, not just blocks.

[...] one could make a silly mistake by rightclicking it with a whole stack of fuel [...]

If the bloomery is unlit, fuel can be removed either by using with an empty hand or by sneak + scrolling.

[...] additional fuel does not provide any benefits...

Adding more fuel increases the speed of the bloomery.