Hi FR I am not sure about down there but grunter definately prefer trench type country over tall structure they love big jew type holes
so I always look for current trenches cased by the pressure wave at the front of wrecks, pinnacles and bombies or the eddie trench behind structures
sometimes these trenches can be 50m away from the tall stuff
in the rivers they prefer the undulating bottom and cockle beds where they sit in the dips under the main current flow and wait for food to drop by
the bottom of mud rivers usually has a bottom that looks like swell lines especially near bends
our biggest grunter like a depth of 14-24m offshore and 3+ in the creeks
cheers