It was previously reported in a thread here that putting a piece of aluminum foil behind a router can increase wi-fi signal strength, and I verified this with the Bluesound app for my Bluesound Node streamer.
Today, because I was having some internet speed problems, I experimented with the orientation of the base router of my mesh network, and found this made a significant difference in the wi-fi signal strength, going from "Good" to "Excellent."
Then for the first time I added a piece of aluminum foil behind the extension router unit nearest my streamer, and that further improved the wi-fi signal strength from -48 dBm to -43 dBm, the best reading I've ever gotten with this mesh network.
Given that an "Excellent" reading is considered by Bluesound to be necessary for streaming hi-res files, this is an important consideration for those doing wi-fi streaming. And perhaps some members who have been disappointed with wi-fi streaming didn't have adequate wi-fi signal strength. I suspect the audible differences (at least with the Node streamer) lie in problems with dropouts and buffering rather than sound quality, but I'm not certain of that or whether that would be the case for all streamers.