Redirect for is_front_page does not work for root URL

I added Themekey to an existing site, so that I can add an "m." mobile site within the site. My first step is to get requests for m.mysite.org to redirect to a dedicated new page that will be the mobile home page (m.mysite.org/mobilefront).

A request for www.mysite.org should not redirect, but a request for m.mysite.org should redirect.

The existing site is configured to have a page at /frontpage as the "Default front page" in Home » Administration » Configuration » System.

I can't figure out how to make a redirect rule that redirects the "front page" when the full path of the front page is NOT used in the request. I can get a working redirect for m.mysite.org/frontpage.

For m.mysite.org, I attempted this with two rules, the second nested under the first.

Rule 1: system:host = m.mysite.org
Rule 2 (nested): drupal:is_front_page = true

This works for m.mysite.org/frontpage, but not for m.mysite.org. Please direct me on the proper second rule(s) that will match the "site root" for m. but not www., which is the implied "front page": m.mysite.org

Thanks in advance,
Lee