Lol, that was probably me re the shell grit, but I have found quite a few targets in that area, but your reference is more specific to gold objects vs coins, which are more likely to be in the gutters further off the beach. Quite frankly, sometimes good finds can occur anywhere, all depends on when they were deposited, what erosion events have taken place, physical barriers like jetties and breakwaters, the wave action, how deep the sand is, and whether the base rock or clays are close to the surface, and so on. The only gold ring I have found was near a jetty on the low tide flats, other lighter gold items have been found all over the place with no rhyme or reason.
The is a guy on another forum that consistently finds gold rings, all have been found off-shore in gutters with clay decomposed bedrock close to surface, a barrier that holds the rings without having to dig to china. That is also in a couple metres of water, so skindiving is a necessity and a very thick wetsuit. That was in vic.
Considering gold is heavy, and for ease of detecting, I reckon working the southern metro beaches (seacliff to glenelg) could be more productive, considering the wave action has mobilised most sand to the north around Glenelg, and as a result, bedrock is pretty close to surface even at low tide on the flats and in the gutters. Probably a good trap for gold, without it working its way too far offshore, and with less digging involved.