It is not common for the Assistant to be the full time director of the top band. In the past, I got to conduct a song for a longer concert, but the head director always ran the ensemble. Even now, I run the band and help with the other classes. My Assistant is a great director, but I believe the HD has the responsibility to run the top ensemble, as its his name on the program. Just like a head coach doesn't let the Assistant run the team.