Please clarify extender magnification for me...

I understand that if I add a 1.4x extender, my 200mm extends to 280.  My confusion is wondering whether the "actual" magnification will be higher?  If my crop sensor camera adds 1.6x to my 200mm, then I'm already getting out to 320.  So will an extender add 1.4x to 320 or just the 200?

Thanks