I would love to hear from the refs when they do and don't decide to give 6 agains. It seems very random and often weighted to one team. I reckon 60% of plays you could probably find some infringement, especially close to the line.
Another thing the refs like to do to disadvantage the underdog teams is when its a favourite and its not clear if the try was scored, they will go onfield decision of try and when its the underdog, they will go onfield decision of no try (more often than not).
In order for the decision to get overturned, its up to the bunker to determine beyond any doubt, that the favourites didnt get a try. and on the other end, beyond any doubt give a reason to overturn the no try decision for the underdog. You go back and watch the games. You will see this happening time and time again.
And to give a further example, how many games do you see when its the favourite, the ref just points to the spot and goes try. No discussion. Whereas the other team, (we will use the Warriors as an example) they send it up to the bunker and they spend 5 minutes looking at every possible angle to find a reason to not give a try, when everyone else in the world can see its a f**king try. Just give it already. It happens ALL the time. Its so obvious what they are trying to do, its not even funny.