Your handpan holds many wonderful hidden treasures. Explore it!
In their book "Hang Sound Sculpture" PANArt reveals the 7 physical sources of sound richness:
Contact ("the contact with the playing surface")
Cosmos ("a cluster of sound that embraces all that can vibrate")
Chorus ("depending on where the player stimulates the instrument, certain overtones will be produced")
Coupling ("the energy is directed to tone fields in the shell that all have the same frequency")
Overtones ("up to a dozen overtones can develop")
Neighbors ("indirect mechanical stimulation of the nearby tone field")
Helmholtz resonance ("the cavity [...] will resound once the vessel wall is stimulated anywhere")
For more insight into each of the 7 sources of sound richness, check out PANArt's book for sale on their website.
Sources: Rohner, Felix, and Schärer Sabina. Hang Sound Sculpture. PANArt Hang Manufacturing, 2013.