To have my recommended configuration you have to have 4 machines/bareMetal/CloudDedicatedInstances. And spread the groups between them.
e.g:
Bare Metal 1
Zero 1
Alpha 1 Group 1
Alpha 5 Group 2
Alpha 9 Group 3
Bare Metal 2
Zero 2
Alpha 2 Group 1
Alpha 6 Group 2
Alpha 10 Group 3
Bare Metal 3
Zero 3
Alpha 3 Group 1
Alpha 7 Group 2
Alpha 11 Group 3
Bare Metal 4
Alpha 4 Group 4 (connect to Zero 3)
Alpha 8 Group 4 (connect to Zero 3)
Alpha 12 Group 4 (connect to Zero 3)
PS. I forgot to arrange the group 4. But you know what I mean.