Here is something to think about..

You ever did an instance a few times in a row, and each of these times 2/3 items dropped -every- single time?

Now we now the raidID is taken into account, so perhaps, if the raidID's are similar, due to being made one after another in a short time, perhaps that could stimulate on certain drops to drop again. *shrug*

Not really sure you could actually use this to your advantage, I don't think you can. But funny anyhow.