My general rule is don't book a taxi, and if it is not there within 10 minutes ring for another taxi. Generally somewhere like ther sheraton is going to get better response to a phoned immediate booking. Youmention people on the rank having more success, if it is busy with ranks full of
pax you'll find that few drivers will listen for radio jobs, this is especially worse with the automatic system where they have to login. When i drove it was voice dispatch and I could at least hear when the operator was yelling for a pick up. But they only yell for a pick up for a VIP customer, someone like the sheraton, DrA who booked the night before is not going to get the same response. The other factor is that when it's busy radio jobs are pretty often no shows, because they usually jump in the first cab that shows up, whereas that is less likely at a sheraton pickup, for example.
Basically if no one is in your area, which is likely if it is busy, say early morning airport jobs, your goingto have great trouble getting a taxi. most taxis in the suburbs will either not take a radio job if they don't want to go to the airport. this happens if shift change over time is close say 5 or 6 am, going to the airport will get them stuck there for at least 2 hours. To make change over, and not pay the next driver penalties, basically means driving back empty. That is also why any driver going to te airport in the morning is going to stay there and get a
pax away from the airport, so taxis will tend to concentrate at the airport in the morning. So it is not that there isn;t enough taxis, just that the business dynamics are based on not starting the car unless your getting paid, as much as possible.
anat0l in relation to the question of driving to Mandurah, if it is outside of the Perth taxi zone then the
pax probably to pay the driver the fare to return to the Perth taxi zone. Of course, I'm not sure if WA have taxi zones and how big they might be.