Installed a Comand Navigation in my 2004 C230 Coupe some months ago and it performed admirably around town and in the Chicago area. Took a high speed trip to Florida last week and I was losing satellites and the performance was erratic. I originally installed the GPS antenna an top of the Comand sleeve, but I guess that there was too much between it and the sky. I moved it to on top of the duct that feeds the center vent. It is now right up against the dash pad and it is working perfectly.

 

The factory suggests the foil cover be removed from the antenna and it be attached to the underside of the dash pad above the instrument cluster.