Name one where it is not. Go do the light test Jon discussed. Every Schleicher fueslage I have looked at is this way. Pretty sure the DG1000 is, ...

You were claiming no glider fuselages have this, having used GPS antennas mounted under the turtleneck in several otherwise carbon fiber glider fuselages I know you are wrong about that.

Here is a game for the upcoming SSA convention... folks there can ask or look to check if the turtledecks in all the gliders on display are RF transparent or not.

Oh the anticipation for the advancement of human (well r.a.s.) knowledge is killing me.... :-)