This thread is part of a larger picture - general antenna
installations. This involves all the radio devices in a modern
sailplane. The problem is the cockpit is a lousy place for antennas
since there's little room, it's full of RF noise and absorbing/
reflecting stuff like the pilot. External antennas are way too
draggy. A good guess is this problem is going to get worse as new
gadgets are added.

Long ago a solution was found for the Com antenna by mounting it in
the fin. If that works for the com antenna, why not PowerFlarm,
transponers etc? The obvious objection is access - the fin is a
sealed box. However, this sport has a lot of very clever people who
have solved worse problems.