I am going to answer inevitable question. Why can it be done in Perth but not in Sydney and Melbourne?
The vast majority of jet traffic for YPPH departs from outside 400nm YPPH. This means that a sequence generated for an aircraft at 400nm is going to be a reasonable approximation because it is less likely to be changed by another jet departure closer to YPPH
This is not the case for YSSY and YMML.
As you can see every departure from YSSY, YPAD, YSCB and tasmania is within 400nm of YMML.
Similarly for YSSY. Every departure from YMML,YSCB,YBBN is within 400nm.
This is why we have to wait till you are about 250nm for the sequence to become stable.