Your question makes sense, however I think you have a little misunderstanding of terminology as it relates to simulcast sites. In a simulcast system each site has multiple towers, which is what creates simulcast distortion. So, in your example, a system with a north, south, east, west site in and of itself does not cause simulcast issues, as each site uses different frequencies. However, the North Site may have 5 towers all on the same frequency, which is what causes the issue. Likewise for the other sites, they will each use different frequencies, however the towers within a site will be on the same frequencies as the other towers in that site. Many times you can click on the site in the RR database and see the various towers in a site, if the locations were submitted to the database.
Now, typically, units will affiliate to whatever site they are closest to or is the strongest, and will change sites as they travel through the area, unless they are site restricted. Using my statewide system as an example, state units (Highway Patrol, DOT, Dept Public Safety, etc) will switch sites as they travel through the state, however local agencies (for the most part) are limited to their county plus each connecting county.
You will only hear traffic affiliated to the site you are monitoring, not all traffic. That said, if a unit is affiliated to your site you will usually be able to hear all traffic on the talkgroup. So, again using my state system as an example, if a SHP Troop A is in Troop G area, and I am monitoring in Troop G area, I will be able to hear Troop A until that unit leaves the area (affiliates).
Hope this makes it a little clearer for you.