I have an X1C with a glass cover on top and the PTFE filament tube touches and slides along the glass during printing with no issues that I’ve seen.
I originally had my AMS sitting on top of the glass but ended up mounting it to the wall behind the printer. I change nozzles pretty often and having easy access to the top makes it a lot easier. In addition the full top view is much nicer than limited to the front window. I also added a riser with extra lights.
I have seen no performance difference either way but make sure to rerun calibrations after you change anything on the printer.
