htaccess force https prevents downstream proxy rule - .htaccess

Question

I'm using an htaccess rewrite rule to redirect subdirectory values as a variable:
Options -Indexes
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/members/*
RewriteCond %{REQUEST_URI} !^/index.php
RewriteRule ^(.+[^/])(.*)$ http://example.com/index.php?username=$1 [P,L]
This works great and uses the P flag so the URL displayed in the browser doesn't redirect. However, when I add the code to force the domain to run via https...
Options -Indexes
RewriteEngine on
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{SERVER_NAME}/$1 [R,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/members/*
RewriteCond %{REQUEST_URI} !^/index.php
RewriteRule ^(.+[^/])(.*)$ http://example.com/index.php?username=$1 [P,L]
...this causes the URL in the browser to change. For example:
https://example.com/myvariable
redirects in the browser address bar to:
https://example.com/index.php?username=myvariable
It does successfully force the SSL, but how can I accomplish both at the same time without the URL changing?

Answer 1

After a ton more testing I was able to determine that removing the domain from the rewrite rule as well as the [P] flag and it works:
Options -Indexes
RewriteEngine on
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{SERVER_NAME}/$1 [R,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} !^/members/*
RewriteCond %{REQUEST_URI} !^/index.php
RewriteRule ^(.+[^/])(.*)$ /index.php?username=$1 [L]