Hi: I had a similar problem with this structure, and was able to solve it this way:
- slaves sites installed on a subdomain like...
www.slave.master.com
- documentroot of each slave... public_html/multisites/{site_prefix}
- deploy tempates folder:: {site_dir}/templates
- Folders and Files: templates as copy file or folder
In that case I needed all the templates to be copied so each user owner of slave could modify it.
I´ve realized that with this structure, JMS creates the file... params_site-id.ini which is ok, but I had a problems with params because the template was not detecting it, even saving them correctly on the params.ini file.
So I had to edit the pacth by changing this...
administrator/components/com_templates/controller.php
On that file, I´ve found...
params_' .MULTISITES_ID .'.ini
and replaced it to just...
params.ini
(think was just on 2 lines)
And it started working. I dont know if it works on other enviroments or how the complete structure works, but in this specific case it helped me after hours of trying to find a solution. Hope this is usefull for everybody, greetings from Argentina...