How to specify pattern for share folder using ACL vfile

My 90-acl.conf file looks like:

plugin {
  #acl = vfile:/etc/dovecot/global-acls:cache_secs=300
  #acl = mysql:/etc/dovecot/dovecot-dict-sql.conf.ext
  acl = vfile
}

# To let users LIST mailboxes shared by other users, Dovecot needs a
# shared mailbox dictionary. For example:
plugin {
  #acl_shared_dict = file:/var/lib/dovecot/shared-mailboxes
  acl_shared_dict = proxy::acl
}

When ACLs were set for particular mailbox I can see that dovecot-acl file were created but I have no idea how to specify a pattern for shared folder like is in the dovecot-dict-sql.conf.ext

map {
  pattern = shared/shared-boxes/user/$to/$from
  table = user_shares
  value_field = dummy

  fields {
    from_user = $from
    to_user = $to
  }
}

My goal is to control how it appears on the client site. As for now is as shared/user@domain/folder/ but I have no idea where it is defined.

Thanks, Adam