No I’m not assuming anything. But the issues I get and many others report reports are typical signs of too high transmission power vs receiver sensitivity.
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Issues paring devices at close range (some devices worse than others)
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Due to high homey transmission power - devices will try to talk direct to homey and not through mesh network. But it then leads to lots of errors. Like wireless buttons working sometimes but not every-time - or switches not switching / off at the right time.
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Devices will jump OVER homey to a repeater further away than homey
all typical signs of not enough receiver sensitivity.
So either the z-wave board is really bad from the supplier - or Homey circuit board layout is bad (it is hard to put that many wireless devices in a box) - or power is simply just too high for the configuration/combination. Changing antenna can help - as it completely redefines the transmission vs receiver sensitivity. The length of cable plays a role and so does the position.
But the easy test is for Athom to open up for manual configuration of transmission power. Now it is locked - (Dev Tools/Z-Wave/Transmission Power - currently locked at 100%)
And for me - the devices that work best are the ones that CAN’T see Homey direct - where I know they HAVE to pass through the repeater. Then ones even in line of sight to Homey have a hard time. (NodeOn switches - Aeotec Switches) - but when they get far enough away - they start working better - through the mesh without direct contact.
btw. I am working as an EE… and do quite a bit of hw/sw design for long range wireless sub-ghz networks 
with TI Chips.
