I followed Tom Knauff's lead with my Discus 2cT, and mounted it on the
outside, on top of the turtle deck. The fuselage is carbon fibre
there, which is opaque to the radiation, shielding me, - and the
antenna is not vulnerable to vagaries of landing as when mounted
behind the gear doors.

While this position will also shield the signal from a receiver
directly below, that is not much of a concern; ATC and onboard TCAS
systems in approaching commercial traffic will have a good signal. To
a large extent it makes one of my concerns, - a mid-air with a jet
whose pilots have their heads down on checklists and approach
frequencies, much more of their concerns.

BTW, I also use a Zaon PCAS on my glare shield for added protection.
Like all the other pilots to whom Tom lent one last winter, I bought
one. I had no idea there was so much traffic out there!