Squawk7700.
......given that much of the traffic comes from Sydney and Brisbane.
And much of the traffic goes to SY and BN. ML tower clears all departures to 5000. When transferred they usually get unrestricted climb to FL240 or their planned level if lower. If you plot all the SID tracks on a map with unrestricted climb to 5000 you'll see it is very difficult to get an opposite direction light aircraft through that.
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