Maybe your start is finding enough food at the surface level of your tank rether than having to forage for it a bit by going beneath the surface level. even my Sand sifter star fish will on ocasion burry its self in my corse sand. I know it will be diving in the fine sand fiji pink is not as fine as sugar sand but it is deffinitly way finer than what I have right now. Other than what you have you can increase flow and cut back on the amount you feed the fish. This may also get the sand sifting star to move in to the sandbed and forage for food more.