How difficult is it to upgrade from Premium Economy to Business Class on Cathay Pacific flights using Asia Miles?

Can anyone give advice as to the “success” of upgrading from Premium Economy to Business on CX flights Perth to Hong Kong & Hong Kong to Toronto, using Asia Miles?

I do quite a few redemption flights with Cathay. I assume the upgrades work similarly. In my experience you have to plan way out (like 360 days, as the availability it released) or wait til just a few days out when they release unsold seats. The second option is fine if you have lots of flexibility, but you don’t get any certainty that a seat on a specific flight will become available.