I have 5 systems for fleetnet zone 1 and five systems for zone 2. The towers are spread across the first 4 groups so that no two towers next to each other, are in the same group. The number 5 groups for zone 1 and 2 I have set up for the fact that i live on the line between the 2 zones. For the tower CC channels for Cobourg and Peterborough that are used in zone 1 I have to lock out. The same for the CC's in zone 2 that are the same for Pontypool and Whitby.
When I am mobile, I enable all systems and enable group 1 for zone 1 or group 2 for zone 2, depending which one I am in. All tower CC's are covered in 5 systems. Those out of range, don't get scanned. While travelling in the Peterborough, Belleville, Cobourg area, usually no more than two towers or systems are scanned. Works out pretty good. Saves space. Rather having 9 systems or more programed. I have 5 systems with all the TG's for the particular zone. The only difference, are the CC's.
When I am home, i disable system 5 for zone 1 and zone 2.