Rewriting a URL outside of WordPress Root

My wordpress blog is installed at domain.com/blog and I have a page with subpages whose structure look like domain.com/blog/page and domain.com/blog/page/subpage.

I want my visitors to be able to go to domain.com/subpage and see the content of domain.com/blog/page/subpage without being redirected to that URL externally, avoiding wordpress permalink rewrites.

I tried using RewriteRule ^subpage$ /page/subpage [L] and the content is being served, but the url looks like domain.com/blog/page/subpage (I’d guess WordPress permalinks are getting to it.)

.htaccess under /blog:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /blog/
RewriteRule ^index\.php$ – [L]

// tried inserting my code here.

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /blog/index.php [L]
</IfModule>

# END WordPress

.htaccess under domain.com:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /blog/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /blog/index.php [L]
</IfModule>

RewriteCond %{HTTP_HOST} ^domain.com$ [OR]
RewriteCond %{HTTP_HOST} ^www.domain.com$

Should I be focusing on wp_rewrite? non_wp_rewrite? Thanks!