Z-Wave communication is two-way, a Command out and a Handshake back. If the receiving device has trouble receiving the Command, it stands to reason that the sending device will have trouble receiving the Handshake back. One solution is to add a Range Extender, but where, sending or receiving device? Why aren't two required, one at the sending device to boost a weak Command and one at the receiving device to boost an equally weak Handshake?
My own experience is that two are required for optimum performance. I wanted Z-Wave in my Pump House, about 100' line of sight from the Main House. One Range Extender gave me erratic performance, but two made it rock solid.
Probably @bcopeland can explain it best but 2 aren't required. In most cases one in the middle is fine to bridge. Yes adding to can certainly strengthen it but 2 aren't always necessary.
"Distance between nodes is not always the criteria for adding more nodes in a network. The Z-Wave radio signals may bounce off metal objects like mirrors or appliances and cause two nodes that are only a few feet apart be completely unable to talk to each other due to reflections of the radio signals. Adding more nodes in the mesh provide alternate routes to nodes that otherwise might be in a dead zone due to these reflections cancelling out the radio signals."
