Yeah, if You have just ice then the studs dig in. If You have an inch of snow on top then the tire flattens the snow and the studs still dig in "allright" but at some point the thickness of the snow is too thick for the studs or the tire thread to penetrate and all you have left is the tire centrifugal force pushing on the snow and the snow slides on the ice underneath it and nothing will help until the snow settles and bonds with the ice underneath - that usually takes several hours.