With 6 teams we would have 15 games in the round robin section so we should better split it in two groups of three teams (= 2x3 games) and let the best two teams each play in the knock out stage.
The disadvantage is that the chance to have an outcome of
A: 4 points
B: 1 point
C: 1 point
is probably quite high. Then it feels a little arbitrary if B or C make it to the KO stage. Open for ideas.