You might try running Zigbee on a USB dongle rather than using the built in version - then you could move the stick around on the end of a long cable. You could also get a stick with an external antenna, which might help. There’s some recommendations in this thread:
However, I don’t know wether it’s possible to disable the Zigbee that’s built into the Yellow - you can only have one instance of ZHA. If not, you would have to use Z2M instead.