That's true. But what about something like mudansha jicho (head of mudansha matters---ji as in koto)?
In order to use "cho", one must be the head of some kind of organized entity
= school, thus, Kouchou
= principal. Toshi
= city, thus shichou
= mayor. Kaisha
= company, shachou
= company president. Kai
= board, committee, meeting, kaichou
is not an organized entity, so cho(u) can't be used. What would be used in such situations is 係り kakari
. Thus, Mudansha (no) kakari
. In a more specific sense, I suspect mudansha (no) shidouyaku
(mudansha guidance) would be used here in Japan.
OTOH, I love things being in their native idiom. English webpage? Targeted towards English speakers? I likes me some "Assistant Instructor" action.
"Web kohai", incidently, would suggest to a Japanese person that there is a "web sempai" who is perhaps in charge of the website. "Kohai" doesn't mean "junior student" in and of itself. Even your Chief Instructor remains someone's kohai.