I don't think your syd-per-drw-syd routing is allowed becuase of the following rule requiring you to have another flight to break up one of the syd-per or drw-syd flights.
Within Australia - only one nonstop/single plane service flight is permitted between the following points:
BNE/CNS/SYD/MEL - PER
MEL/SYD – DRW
MEL/SYD - BME