just to get some perspective on the area / directions etc:
Google Maps
a couple of interesting factors, and I’m sure those here who are familiar with the area, will guide:
* The visibility on streets look to be quite good - so IMO it would be easy to spot anything or anyone ‘out of place’ .
* Seems like the Crabbs lived at the very end of the bitumened stretch of Benaroon Drive. I recall a mention of hearing a vehicle turning on gravel, so that would seem feasible imo. .. and perhaps it may have been the ‘turning around on gravel’ at that time of the day, that made them think it was the Postie ( and not necessarily the actual vehicle type / engine sound )
* Laurel Street ( where Mr Chapman lived) is a very simple 3 min drive from Benaroon Dr & comes out right near the Kendall Tennis club - but it does have exit option via Jackson St too
just my ponderings ..