A deeper substrate is definitely preferred by the vinegaroons. If they don't have a few inches of substrate, provide a hide. A nice sand/coco fiber substrate seems to work pretty well. There are two individuals where I work and we are keeping them differently. One has a substrate that's about 10 cm deep and the other has a substrate that's about 2 cm deep, but with a hide. The one with the deeper substrate went to town and burrowed to the bottom overnight. It seems to be pretty happy.