Thanks, it makes perfect sense now!
We don’t have creation rights as a part of custom access templates since there is currently no way to enforce a parent for a newly created Entity. This means you cannot grant permission to create Interviews for a certain Position — only to create Interviews in general.
To unlock your use case we are missing two things:
- Specify who has the right to create Entities of a DB without granting read access to all the Entities of the DB.
- Mark a certain relation as required and do not allow “orphans”.
The first part is planned for this year as a part of Database access. The second part is more tricky but, I assume, less pressing.
The current workarounds would be to use publicly shared Forms to create Interviews or use Contributor Space access. Neither is great, I have to admit — that’s why we are working on DB permissions 
.