[CentOS] SELinux - different context on subdirectories

Hi all,

I have created a directory /srv with the following SELinux context:

system_u:object_r:var_t

Now I want to create a subdirectory within /srv which should get a
different context.  So I tried to set e.g.:

semanage fcontext -a -t samba_share_t /srv/samba
/sbin/restorecon -v /srv/samba

but the context is always reset to:

system_u:object_r:var_t

What am I missing?

Best Regards
Marcus