On the matter of basshorn size, in my admittedly experimental amateur's opinion here's my 1¢ worth. If a horn is too small and the designer tries to push bottom end extension too low, the compromise requires either efficiency will be low or response will be lumpy, or both. Distortion is proportional to excursion so if a horn is compromised, distortion goes up. Response, efficiency and bass extension are proportional to size, so if the horn is small you have to sacrifice at least one of those things. There is no magic bullet.

A small basshorn can be made right if deep extension isn't needed. You just have to design it right for its size and not try to make it try to be something it's not. Don't try to fit 10' of path length in a monkey coffin size box. That's how I see it but WTFDIK.