It is somewhere very well explained but my understanding of AF policy can be quickly summarized :
firstly, the more you pay (discounted fare have nearly 0% uprade potential), then the highest you are in the FFP (platinum will be in the top list)...
This depends on the filling in your current class...and the availability of the upper class...

In any case, this is definitively not depending on your smile while asking the ground AF staff.....(hum... this should penalize ). The best bet is to never ask !!