Unfortunately, I have rarely seen any research where the person burying a Treasure has been available to tell me where , and how deep they buried the Treasure.
What results are you talking about? It was a Dowser on this forum that gave that depth for the location they provided. Do you think the Dowser purposely misled Salvor 6, so they could go to the site and dig the Treasure for themselves? Is this what you would do? If that was the intention, why bother to even give the site location?
You are right, the majority of small Treasure Troves were not buried deep. But, depending on the environment, overburden builds up, the water table rises, and sand turns to quick sand, and the Treasure sinks deeper and deeper over time. Add, floods, Earthquakes, land slides, Dust Bowl, etc, you best be prepared to dig deeper than the Treasure was originally buried. I know from lots of experience. Dell