Ianpizza I used to work there so I'll explain it to you. Some things have changed operationally from when i was their from 2000 to 2007 (full and part time), so I'm not fully up to date with the day-to-day operations. But I still have a lot of connections and the channels and tower locations haven't changed.
You are correct with the pairings that you have listed that are mainly used for patching units into the hospitals. MED 3 is also used for Mid-State for those units up in the Meriden / Wallingford area. MED 6 is used for those units coming from the southern end of the region in North Haven or the southern End of Wallingford. MED 5 is located on two towers, one in Wallingford and the other on the Shoreline. MED 5 gets more use up in the Wallingford westside area when needed. Also all the MED channels can be used as tactical channels with or without a repeater, they can be remotely turned off by the dispatcher. MED 6 can also be used if a unit coming in from the Shorline or Middlesex area needs to patch when they are out of range of the MED 4 & 7 radios. MED 8 is also used to patch to the USVA in West Haven.
The main reason for the pairing like you have listed is because of that tower's location to a specific hospital / clinic for use with their backup radios, which just work as a control station of sorts. They also have them set up this way to make it easier for the ambulance crew to patch in and also to help out the dispatchers from having to keep on connecting up the hospitals to the patch lines. like any other radio.
There is a little known fact about South Central, you can patch any hospital in the region to any MED 1 through 8 channel. For example, you can hook up Griffin Hospital in Derby to MED 2 on the Shoreline if need be (yes there was a patient from out that way that wanted to go to Griffin, needless to say the doc at Griffin said to go to the closest place; patient should have listened to the ambulance crew!)
C-MED New Haven has several sites through the 18 town region. Four of the sites have MED 10 on them, the primary dispatch channel. MED 9 is not utilized in the region for dispatch, however when I was there it was talked about using both frequencies as a low powered tactical on-scene channel but that idea never flowered. We also had the old MED 11, 12, 13 & 14 channels as well. Only MED 14 was used for dispatch up in the northern area of our region due to the fact North Central also dispatched on MED 10 (different PL) and used to stomp all over the units up there. But they got rid of it because of some complications.
Here are the tower list with the MED channels on them, a "R" after means that channel's base radio is repeated.
Valley (Seymour) MED 10, MED 1-R, MED 6
West Rock (New Haven) MED 10-R, MED 4-R, MED 7-R
East Rock (New Haven) MED 6-R
Cook Hill (Wallingford) MED 5-R
Meriden MED 10, MED 3-R
Shoreline (Guilford) MED 10, MED 2-R, MED 3
WHVA - MED 8-R
Eels Hill (Milford) - MED 8
Hope this helps out.