"The main principle Huygens is famous for, at least as far as folded horns is concerned, is the topology of a 45 degree reflector, as you state."

Huh? Huygens is known for pendulum motion, centrifugal force, gravity and wave motion. He is famous for a lot of things.

"However, a rounded bend, and not just a rounded bend but one with a rounded inner corner of relatively wide radius compared to the wavelength being passed, ideally allows the wave to pass without being reflected at all."

A large bass horn is many wavelengths across at midrange so inside walls are reflectors. Midrange sound bounces all around in there. Get a clue.