Setting the volume to 8% could potentially set it to zero as each phone only has a fixed number of steps. For example there could be 10 distinct volume steps such that there are bands where each value within a 10% range maps to the same value.
If you are wondering why it uses percentages in this case (that would be a good question). It's because each device is different so it's a portable way to map a rough volume level across devices that have different numbers of volume steps.