I think it's as much about the correct physical location to be as close to the readers as possible as opposed to the shaded area being anything special. Could be wrong though.
Sort of... Some screens are coated with a metallic layer, and heated screens are a problem. Those screens typically have a larger black/shaded area for the tags and garage openers. I think you will be fine in a 4200 - I have it in the clear zone to the left of the mirror on the QP, and it works perfectly.
I keep a DART tag in mine an it is tucked up behind the mirror, never had a problem with it and it is identical to the French unit so I will just swap it on the clip. The Italian one uses a velcro pad but I dont imagine I'll stick that on but then maybe it will be easier...
Having recently used both, I'd say the Italian one worked better...barrier lifts well before you get to it. Toll lanes are designed so you don't have to stop at all. French one was a bit temperamental.
Update from Chamonix. The tag does NOT need to be in the shaded black area behind the rear view mirror on a 4200. You can place it in the clear area of the screen.
Update from Chamonix. The tag does NOT need to be in the shaded black area behind the rear view mirror on a 4200. You can place it in the clear area of the screen.