I forgot to post this. I got so involved in the other message.
I don't know if anything below is still relevant
I'm not familiar with any Firewall plugin, and I presume you're referring to a plugin that does NOT come in the default WP install.
I used the AutoMagic buttons in BPS to create one default and one secure .htaccess file. I don't recall the word 'Master' arising. If it did, then it didn't register in my mind.
That dialog also gave me notice that it could not create a (whatever) .htaccess for the wp-admin directory because it did not (and it doesn't) have an .htaccess file.
I have two WP installs in a folder one level below its root; two domains. Neither has an .htaccess file in the wp-admin folder.
For each of these WP/BPS installs, I activated the BulletProof Mode for the domain.com/wp/.htaccess only, since that's all I have.
In the bulletproof-security/admin/htaccess folder for each of my WP installs there are the following versions of .htaccess files: