Well, I'm not a forensic tech, as you know, but I would think that the much more densely populated areas, and high traffic areas, like the freeways etc in Melbourne, would have a much higher ratio of phone cell towers per square kilometre. This, in turn, would allow much more accurate tracking as the phone was "handed off" from one tower to the next.
But out at Brookfield, we have the Brookfield tower near the exchange on Upper Brookfield Rd, the Kenmore Tower up in the main Kenmore shopping centre about 5Km away in one direction, and the nearest in the other direction would be the one at the Vet Farm at Pinjarra Hills - also several Km away. Brookfield is not surrounded by a close network of towers, compared to somewhere like a CBD, or that area in Melbourne where the accused drove Jill Meagher's body. Also, Brookfield is quite a hilly area, so line-of-sight connection to towers is quite variable. The BC house would be in direct line with the Telstra tower at the Brookfield exchange, and it MAY be able to connect to the Kenmore tower which is on Moggill Rd in the centre of Kenmore, right on the bend opposite the OLR church.
But the GBC phone records show the locations of towers from Chapel Hill, Mt Coot-tha, Kenmore, etc etc, and all with the identical timestamp. So that probably would be consistent with the phone just registering the database of all towers within a several Km radius at that time, as per those links I just posted above.
EDIT: Thanks Judicious - you posted while I was still typing
Yes, and in particular, the lay of the land around Brookfield, being quite hilly, would be very different from the freeway etc in Melbourne. And as I said, the number of towers per square Km in Melbourne's high population suburbs would be much greater.