Yes, I agree with your theory, but I think there is a compromise, 1st of all, squared off trailing edges look hideous in my opinion on a "flat" stab. I would feel like I left it unfinished. Ideally the elevators and rudder would be tapered, but now that is a lot of sanding !! Actually an airfoiled tail would be the best , like the ailerons, that would be my choice. But I feel that with a model such as this, not designed for speed, the imperfect aerodynamics will not be noticed, I have done this on all my models that have a "flat" tail. If I remember right, most instructions "goldberg, midwest, great planes, etc" show them rounded.