C1 and C2 can have “Perimeter” gas sites.
C3 and C4 can have “Perimeter” and “Frontier” gas sites.
C5 and C6 can have "Perimeter, “Frontier” and “Core” gas sites.
For a description, see the tab named “Gas Sites” in the link below.
https://docs.google.com/spreadsheets/d/17cNu8hxqJKqkkPnhDlIuJY-IT6ps7kTNCd3BEz0Bvqs/pubhtml#