Although I haven’t experienced “grunge” with my Lumin U2 Mini I can support the proximity issue. I use the Amplifi Alien router and mesh and the phone app helps to locate the mesh position to where the signal is the strongest.
Mine (unfortunately) sits on the floor with devices hard wired from there but after going through the process I’ve rarely experienced drop outs or stuttering during playback while streaming.
The one issue I don’t like about mesh units is that they seem to occasionally lose sync with the router. Although I still have service unplugging/restarting is a quick resolve and never takes more than a minute. The display on the front of the unit notifies you when this needs to happen.