Freebeard,
For sure I don't want to over reach, but I don't want to under reach either.
As the tail is fixed, it is limited in length due to practical reasons. Obviously like everyone I want it to be as effective as it can be in that length.
I am not quite sure I am following "angle of the flow to lengthwise of the trim," could you please reiterate?
What I think I know from Hucho's book was the necessity of window flushness decreased the further back you went, stating that a 5mm inset glass did not increase drag at the rearmost window. That led me to believe the boundary layer was built up enough to accommodate the slight bump. However I don't know if parallel glass and parallel panels with a transition translates to following a taper with a bump.