I also have a 2016 Homey and live in a quite small house where Homey is located right in the middle. No more than 8 meters to the farther zigbee device. Yet, without the antenna mod, barely I could reach 3/4 of the devices. Now, I even have a zigbee door switch right outside on the main gate (which is metal, too) and no range issues anymore.
Another good thing to have is a whole hip of zigbee repeaters (those are mains powered devices) I have none of the by the way but the antenna mod helped.
See here: Homey Pro Antenna modification - #26 by danone
You should try setup your wifi on channel 11 as that would give you the least interference. See here explained Wifi and Zigbee: https://support.metageek.com/hc/en-us/articles/203845040-ZigBee-and-WiFi-Coexistence
Hope this helps a bit.
