Roku keeps disconnecting from wifi

I have 3 Roku Express 4K+ units operating at WiFi-5G and found them all to be very sensitive to position and orientation, even when located fairly close to my WiFi router. Mine were all initially placed on a flat surface (TV cabinet, shelf, etc) near the TV with marginal results. I was able to easily tune the position of all devices to improve the transfer-rate from 20-50 Mbps to over 150 Mbps by simply propping them off the cabinet/shelf using a small piece of cork about 1/2" thick to create an air space around the entire unit. This significantly improved the signal-strength and transfer-rate for me.