I had some comments about my views of your Norfolk Island reception... I've just marked... what I have noticed happens on these QLD and NSW coast openings. I have noticed this since I was doing the VHF weak signal column in Amateur Radio Magazine about eight years ago, and getting reports from QLD stations, I would have a look on the maps and see what was happening.

Most of them happen along a Low Pressure Trough, running along the QLD ranges usually, a way back from the coast a bit, stations must be on the east side of the trough to get the conditions. The warm and moist air being drawn down from the north along the trough and the winds coming around from the north of that High Pressure Cell, I think is what has helped your signals along there. I have seen this before also on some paths to New Zealand, which I think I have documented on the World Tropo Ducting pages with images.