For a Star Formation, you need five or six aircraft. On this schematic, you see a Star Formation with five aircraft: three in Line Astern position with two planes in Vic, on the wing of the before-last airplane flying Line Astern.
With six aircraft the ‘base’ becomes longer – there will then be four planes flying Line Astern. The two on the wing will remain next to the before-last plane in Line Astern.