Primary and secondary intake port question
 

Why are the primary ports smaller than the secondary ports? I realize intake charge velocity will be greater on the smaller ports creating better low end power but are the secondary ports closed off then? Also when the secondary injectors arn't firing are the secondary ports still pulling in as much air? What would the repercussions be if both ports were the same size? I really feel like I dont have a grasp on how this exactly works. I tryed searching but came up short on these basic questions. Thanks in advance