I had an issue with some Z-wave devices that insists to be disconnected from HC3. Have tried to relocate HC3 (as much as possible w/o irritating my wife) without success, always had some disconnected devices.
But during the relocation have noticed that in some specific spot all devices have been connected. The problem to achieve full coverage, requires accuracy of ONE millimeter!
Have tried to understand, why? I have my own SMS system connected to HC3 and when a specific corner of HC3 has touched the antenna (accidently) I have a good coverage.
So....
I took a piece of metal and actually stuck it under HC3 like antenna (see below), now I have an excellent coverage. It's sound like a joke, but it's not a joke at all.
After that have found an image of HC3 board, and YES, the Z-wave antenna is actually located on that corner of the box.
Of course, will try to get a proper 868Mhz antenna to attach instead of current solution, but hey! it does the job.
By the way did the same for Zigbee antenna also and again, a good improvement.
There is a good logic behind that. Since HC3 has internal on-board printed antennas, any piece of metal could work as extender. Of course, it should be placed correctly otherwise it will cause interference. Let's say it's like wireless charging that we are using daily for our phones, as you know you should place the phone in very specific area.
Here the actual image (please forgive me for the mess, the cost of moving the equipment around)
In addition, I recommend using Z-wave repeater NEO Coolcam Z-Wave EU Repeater Sensor Compatible Zwave System 700 Series Home Automation - AliExpress
It does work very well (not like AoenLabs extender which always shown as unconfigured device on all Fibaro systems). This extender configured and all parameters could be defined. Best repeater I ever had.
I am very curios if it helps to others... please let me know if it works for you too.