Yield/Quantity question

[Nai`Ji]

Ok, so here I am making some fossil tempers. Using lead clusters as the root ingredient, the process uses 1 lead per combine and yields 3 vials. Now, I run out of lead but have a few malachite left over. So I go ahead and use them. What is weird is that I started with 3 malachite, did 3 combines and still had 2 malachite left over. What's the deal with this? Is there something I'm over looking? Is there some kind of usage quantity or yield formula based on trade level or reagent types? TYIA :)

[Ausversucht]

The recipe will also utilize tin if you have any in inventory. May want to check that.

As a general rule it will use whatever you have the least of first for refines (it goes by stack size).