How to add rewrite rules and pagination to retrieve attachments files?

Based on the comments of @Milo and using the rewrite analyzer plugin I found what I understand as a conflict in the rewrite rules?. The following url:

exams/high-school/city-name/subject/math/

matches the following rules

Pattern:
    (.?.+?)/page/?([0-9]{1,})/?$
Subtitution:
    pagename: exams/high-school/city-name/subject/math
    paged: 1

Pattern:
    (.?.+?)(/[0-9]+)?/?$ 
Subtitution:
    pagename: exams/high-school/city-name/subject/math/page
    page: /1

Pattern: 
    exams/([^/]+)/([^/]+)/subject/([^/]+)/?$    
Subtitution:
    pagename: examns
    level: high-school
    city: city-name
    subject: math
    page: 1

The last one is the one I’m trying to create. I’m not an expert in the rewriting rules but I think the second one was activating first and producing the wrong redirection to http://www.example.com/exams/1 or http://www.example.com/exams/2.

So, I changed the second of my rules to:

exams/([^/]+)/([^/]+)/subject/([^/]+)/page/?([0-9]{1,})/?$'  => 'index.php?pagename=exams&level=$matches[1]&city=$matches[2]&subject=$matches[3]&pages=$matches[4]

Note the var as ‘pages‘ in plural. It’s working properly. However, the rewrite analyzer plugin is not detecting my rules. ‘?’

In fact, if I change ‘page’ by ‘pages’ or ‘whateverIwant‘ and register that varname and getting it in my plugin:

$args = array(  'post_type'         => 'attachment',
    'posts_per_page'    => 2,
    'paged'             => ( get_query_var('whateverIwant') ? get_query_var('whateverIwant') : 1 ),
    'orderby'           => 'post_title',
    'order'             => 'ASC',
    'post_status'       =>'published'
);

Also work!. So, the first set of rules I created was in conflict with something inside wordpress. I have much to learn.

PS: I will accept any question with a solid argument solving this problem.