Some pretty big nuggets have been found within a few inches of the surface with detectors, but mostly it seems small nuggets are being found, although that's probably because most of the big stuff was found long ago, there was a nugget of a couple of kg's found not really that long ago, the "Fair Dinkum" nugget, think that was only down a few inches & found with a Minelab detector.
Also in another section of this forum it was posted about a 5oz nugget that was found not that long back with the TDI Pro Oz detector with 20" coil, the nugget was down 32 inches, so some good size ones are still around & can be found at pretty much any depth.