301 redirects within different WordPress set up

Hi there,
I have a bit of an unusual set up of WordPress and as a result seem to be having issues getting 301 redirects to work correctly.

The front page is http://www.researchnutrition.com.au which is just a site select page, whereas the “home” page of the remaining site is http://researchnutrition.com.au/retailers-consumers

Now I need old URLs to be redirected to the right place (URL page names/structure has all changed)
eg.
a previous URL: http://www.researchnutrition.com.au/retail/contact-us/
now needs to go to this page:
http://researchnutrition.com.au/contact/

However when I add this to 301 redirect it automatically appends the secondary ‘home’ page, e.g. it ends up going to http://www.researchnutrition.com.au/retailers-consumers/contact-us/

So I need to strip that retailers-consumers from URL and not sure how to go about doing it?

Any help or insight would be much appreciated. Many thanks.