After looking at the results at the weekend, I noticed in the super rugby quarters, URC quarters and the last round of the premiership, all games where won by the home team. In the top 14 it was only 4 out of 7 won by the home team.
Not 100% sure what my question is but thought it was interesting
You have to effects here and i believe you are combining them. Typical 1/4 finals. 8 teams, lets rank em: 1,2,3,4,5,6,7, 8.
Generally you get something along the lines of 1v8, 2v7, 3v6 and 4v5, AND 1, 2, 3 and 4 play at home. That is done so to reward those who finish better during the regular season.
So when you say that 1,2,3 and 4 won, well, you shouldn't conclude they did because of home advantage. The evidence suggests they were better to begin with (hence the rank).
How much is because the team is better and how much is due to home advantage? god knows. You could do some sort of stat analysis. I know that's been done in other sports, havent seen one for rugby tho.