Subdomains not using the post slugs

My cPanel subdomains are working fine pointing to the blog home page but are not able to carry the sub urls of the subdomains. e.g brands.advantages.us works with advantages.us/brands but brands.advantages.us/x is not going anywhere while advantages.us/brands/x is live.

also if this can be done with reversing the redirect then how can my folder brands start chewing the inner files for the subdomain. can it happen for an external independent domain, where the wordpress.com documents are already translating in domain mapping?