Haha, this I can help with.
I've just pulled out an MOT failier for my Calibra Turbo and the legal limit, or the maximum limit allowed for an MOT is something like 40mm of the window. I'll type it word for word so you can see yourself.
"Windscreen has a sticker or other obstruction encroaching into the swept area by more than 40mm outside zone 'A' [9.3.1e]"
So there you are, if you have a sunstrip, dont go over 40mm of the wiper sweep area of the windscreen