This morning I asked AJ about the reason for this fence.....here his answer (I did asked permission)
AJ Answer- On the stab fences what I found was it seemed to lock the tail on when in pulls and pushes. The model isn't unstable when in normal flight but I did feel that in radii it kept the plane tracking a little straighter, and of course no problem with posting it on RCU...
So there you have it from the top US flier.