Now that the empennage fairing resin has been able to properly cure overnight, today I carefully removed it from the tail section and sanded back the edges. When reinstalled onto the aircraft it is amazing. All the "pillowing" gaps are gone and the faring sits flat all the way round.
I'll do a bit more sanding to get the edges feathered a bit better, but this is a great improvement.
The faring, with hardened resin along inside mating surfaces
