I have had good OP upgrade success (as well as work colleagues) on the CPH-BKK route. But I'm EuroBonus Gold.

Sometimes however, I have NOT got the OP upgrade when it's been clear that OP upgrading was done. So, it's never a 100% guarantee that it will happen.

Seasonally, the months of July, August and Christmas time seem to be best. That's when there are fewer Scandinavian business travellers but a lot of leisure travellers.