My strategy depends on the item recipe and the need for new tier item.
When I reach a new tier, I really need the new tier refined or not so I use wathever I have and pray.
After that, when I try to get new refined item I proceed this way:
Craft previous tier until I got 2 refined.
Craft new tier with all non-refined but 2, (and pray).
If I dont got a new refined item I use the 2 refined then the last 2 non-refined, this process minimize the probability to get 0 refined item (so it maximize to probability to get at least one).
If in the first process you get a refined, the second process doest really matter. Once you have 1 refined of the new tier, you don’t have to maximize the probability to get at least one. I think you should maximize the average number of refined item you will get. Using 2 times 1 refined and 1 non refined is slightly better 2 refined and 2 non refined is slight better but not very significant (~0.005 refined item on average).
Maybe you should try to use 2 refined then 2 non refined, with the same goal as previously, because in fact the probability to get at least 2 refined new tier item is also important if you want to apply the same process for the next tier.
Here are the figure:
with 2* and 2 non *
the probability to get:
- 0 refined: 38.25%
- 1 refined: 55 %
- 2 refined: 6.75 %
- at least 1 refined: 61.75 %
- refined item on average: 0.685
with 2 times 1 refined and 1 non refined:
- 0 refined: 42.25%
- 1 refined: 45 %
- 2 refined: 12 %
- at least 1 refined: 57%
- refined item on average: 0.69
As you can see, If ressources are a problem you should not wait for 2 refined, and craft with wathever you have.