Masking login area doesn't work properly with sub folder installation

My site has wordpress installed in a sub-directory /wp/ , this is set by the host. I have changed the login URL in defender to https://domain.com/wp/mycustomlogin however https://domain.com/wp-login.php still works and redirects to https://domain.com/wp/mycustomlogin
Also setting the redirection URL uses the wordpress root, so that's not accurate either, it redirects to the folder with WP installation (https://domain.com/wp/)