A “nice” detail on zwave, is that is can use a maximum of four hops (EDIT: NOT including the controller and the end-device, so four repeaters). zwave won’t look for the ‘best path’, it will just look for a working path, and if that works, it will keep using that until for whatever reason it doesn’t. Unfortunately you can’t ‘hint’ it to use a specific path. Sometimes the chosen path doesn’t seem logical to us humans, but if it works, then it’s okay right? 
What I’ve seen happening in my own situation is that some devices ‘talk louder’ than others. For example. The Homey sphere is a really lousy range (on all protocols I think)
My apartment is about 10 by 10 meters. The Homey sphere is in the approximate centre. It however can’t directly reach a radiator valve on the far side of my apartment (roughly 4-5 metres in a straight line, a few plaster walls and some light wooden furniture between it).
For this purpose I purchased a smart plug and started experimenting with it. When I set up the plug as far away as I can from the valve (about 10 meters from the valve and about 5 meters from Homey) (No walls, only some furniture between it and the Homey sphere).
There is more furniture, the Homey sphere and the same walls between the smart plug and the valve it can still use it as a hop without any issues.
(( edit - zwave allows up to four repeaters between the controller and the end-node ))
