Have you tried putting the whole unit under the clear patch?
My gps camera detector goes under the clear patch, and my sat nav is on the right of the windscreen, kinda towards the drivers side window, so it can recieve the signal through that one, as it doesnt have the coating on it.
It's a bit of a sh!t really, really limits where you can put stuff, unless you buy an external gps reciever ( usually either bluetooth or wired) and mount it somewhere like on you parcel shelf, or some people like to put it under the black plastic bit behind the bonnet ( where the windscreen wipers are)
Edit:
Bugger, didnt read that lol, factory fitted: dont know lol
"Has" on here is a gps wizz, try pm'ing him?