What is the upgrade 'algorithm'?

Do we have any hard information on how Qantas makes upgrade decisions?

I've noticed I seem to get less upgrades since dropping from Gold to Silver, but maybe it's due to requesting them more on international flights...

Anyway this got me wondering, do we know the decision tree that Qantas uses for ugprades? For example, are all platinum requests served before gold, regardless of when the request was made? If so getting in early would only help you compete for an upgrade against people at the same FF level.

This is just one possible example, but they could use a more complicated scheme.