I suspect the limit that you are probably up against with your reconstructed ear canal is not just the necessary power of the hearing aid to overcome the big conductive hearing loss, but the much more reflective ear canal wall compared to a typical eardrum which is probably dramatically increasing the chance of feedback and that is in turn limiting the gain.
If you can’t get any sort on bone conduction solution working, and Phonak didn’t work, maybe give Oticon a try.