Recently I had this question on the website formerly known as Twitter.
I thought this was a very interesting question because while whether a seat comes down to the final two or not doesn't have much to do with how close the seat is, it's something we don't think about much in federal elections. Every vote is thrown by the AEC to the final two candidates, but in some cases it doesn't reach the final two until after the seat has already been decided because a candidate has crossed 50%. Indeed, in a rapidly reducing number of seats the contest is decided on primary votes and the preference throw is entirely academic to the result.
Contests don't get thought about in these terms so much because every vote is present in a notional final two soon after it is counted via the notional two-candidate preferred. This gives a single indication of the margin of victory. It obscures the nuance that a candidate who finishes on 54% of the final two-candidate preferred might have even crossed 50% before the last exclusion then done badly on the last lot of preferences, while another candidate might have needed a trickle of preferences to get over the line yet got so many preferences that they finish up with a 2CP of 68%.
