The Top Mafia Gospel According to Zynga: Assign your best mafia members to positions within your mafia. Each position has a unique bonus which can be greater depending on who gets promoted to that...
It is either because people have not added others to their top mafia or Zynga which frequently has server issues is having trouble displaying top mafias.
Go to my mafia them my mafia members them click promote besides the member you want to include in your top mafia.on the new page choose their position.