Correct. You have to do it separately for each domain.
Since the files viewable/readable from the web are those found in /domain1_com/ folder. You can not do it for the /public_html/ folder as the files inside are not read (like trying to use same protection files for folders /domain1_com/ and /domain2_com/)
Since the files viewable/readable from the web are those found in /domain1_com/ folder. You can not do it for the /public_html/ folder as the files inside are not read (like trying to use same protection files for folders /domain1_com/ and /domain2_com/)