Htaccess redirect without changing url works but some content within enfold fail

I want to redirect domainA.com/folder/ which originates from an older WordPress installtion (not Enfold) to domainB.com/folder1/folder2/ (Enfold within WordPress Network) which is the link to the page within my new wordpress installation wihtout the url changing.

I have managed to achieve this with the .htaccess file inside domainA.com/folder/ which reads:

RewriteEngine On
RewriteCond %{REQUEST_URI} ^/folder
RewriteRule ^(.*)$ http://www.domainB.com/folder1/folder2/ [P]

The Rewriterule [P] (proxy) flag does what I want and redirects the page without changing the url but some of the content within my Enfold WP template such as the advanced layer slider and icons fail to load.

I assume this error is due to some sort of conflict with WP’s native htaccess code and I also suspect it has to do with the lines:

RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

I have experimented with adding the first, third and fourth lines to my code but it doesnt work. Does anybody know how I could resolve this issue?

If it makes any difference the wordpress site I want to direct to (domainB.com/folder1/folder2/) is one whithin a WordPress Network.

For the moment I have changed the [P] flag to [L] flag which redirects and works but changes the url.

Any help or advice would be much appreciated. Thank you!