Dropbox overrides file permissions debian9 (linux)

Since the start, that we added a dropbox daemon on our sambaserver, we face the issue of overriding the file permissions by dropboxusr. For new created files, via the dropbox, the permissions are set to:

-rw- -r-- --- dropboxusr sambausers  <filename>. Even if the set bit is set ON the directory. This means that all are server users (members of sambausers) cannot edit these files on their network drive (win10).

Our goal is to achieve:

-rw- -rw- --- dropboxusr sambausers  <filename>

we tried al lot suggestions of the dropbox community the last 5 years:

a) editing the /etc/init.d/dropbox

b) setfacl suggestions

But none of the ideas worked on our Debian9 system. So we are still looking for the ultimate solutions. BUT

we have already for a long time a workaround I want to share:

as a root user we setup a crontab that runs every 5 minutes and chmod -R g+w <dropbox root directory>.

It is not a nice solution but it works until we hopefully one day have the real solution for the problem.