Qantas is pretty stingy in giving out premium (F/J) awards. I can understand the F awards, as there are only 14 seats in the cabin. But they should be a little bit looser in J, but this is not always the case. I was able to get an F seat, tinkering around with my departure dates +/- a few days, a month before departure.

They tend to release more seats as time draws near to departure, depending on the load factors. It's sometimes better to try dates closer to departure.