YUP the front heated windscreen do block GPS signals.
My car have just that, 100s of very fine lines running down the windscreen. They can only be seen when looked at closely. Not alot of cars have them for some reason, they do work nicely though.
Mine didnt have lines on the left and right side of the screen...about 5-6 inches from the sides. You can try placing it just there on the side, it work ok on my car then.