BN2T - 4S tail section

[1.86EPR]

On the Defender 4000 aircraft, (a turbine aircraft based on the Islander) located high on the tail fin there is a small 'tail plane'. There appears to be small ice boots on this, however the surface itself doesn't move. What is the function of this 'tail plane'?

[Tinstaafl]

Not a Navaid receiver is it? I've seen various ones that are a thick wire loop or are solid surfaces mounted both sides of the fin.