I compared horizontal tail from rotax618 to my Skyboy. His tail if I remember correctly about 20% bigger, but his engine is two times smaller and it's sitting below the wing.The Australian Boorabee aircraft have a similar layout, two abreast seating, strut-braced high wing. HBA member @rotax618 designed it, and he has commented on his ultimately successful addition of VGs to address some problems. Any others problems that were avoided or fixed? Any remaining handling characteristics that are just inherent in this configuration? Maybe there are other lessons applicable to the FlyBoy.
Could that simply be that tail size is simply very important for airplanes with this configuration? After all the rocket doesn't need tail at all