The only thing I can recommend is to make sure the Z-Wave antenna is mounted high. Also, play with the orientation - vertical, horizontal, etc.
HS3Pro Running on a Raspberry Pi2 (Raspbian)
57 Z-Wave Nodes, 162 Events, 293 Devices
UPB modules via HAI plugin/panel
Plugins: Z-Wave, BLRF, HAI, HSTouch, weatherXML, EasyTrigger
HSTouch Clients: 3 Android, 1 Joggler