I've seen somewhere on this forum that BeatSonic fin shark antenna doesn't fit BRZ. And I understand why - BRZ antenna base includes sat radio antenna, and the base is bigger compared with FR-S. I can snap a picture of mine to compare, if someone will post FR-s base here.
Because shark fin will cover up sat radio antenna and will interfere with reception, I opted out for Cusco 2 inch antenna. Looks like every other car right now has those fins - not cool anymore
http://www.ft86club.com/forums/showthread.php?t=8848
P.S found that thread with BeatSonic antenna issue:
http://www.ft86club.com/forums/showthread.php?t=7804 And they have removed BRZ from Beat-sonic site as an option for this antenna too