Hi Brett,
While I haven't had specific experience fishing up around your area, I do know that in the areas I have fished (Mackay/Whitsunday islands), GTs are often inclined to come into very shallow water to feed if the bait is there and conditions are right.
We have observed plenty of times over the last 10 years or so, GTs over 20 kgs feeding in water so shallow that their backs are breaking the surface. Mostly this seems to occur when the conditions are dead calm and tides are big. The actual locations we find this sort of activity tend to be sloping rock shelfs strewn with boulders in close proximity to headlands. If there is some sort of deeper channel nearby, then that probably helps. I'm sure deep water nearby scenario would give the bigger predators easier access to the shallow grounds and so hopefully they might be a little less flighty.
To be fair, I suspect the shallower water under 5-10 metres probably attracts a smaller class of fish, but certainly, I reckon there is still a good chance of encountering larger fish from time to time in the shallows.
I'd be interested to hear what other members have to say on this subject.
Cheers
Angus