Parliamentary Voting System and Constituencies Bill

I have just three questions. First, why will it apply only in the final seat? Why would it not be possible for there to be a tie on the way there? Secondly, when it says, "““smaller or smallest actual electorate””," what is the difference between ““smaller”” or ““smallest”” actual electorate? Thirdly, does ““smaller or smallest actual electorate”” refer to the total electorate in that part of the United Kingdom, or to the electorate that is left? I am more than happy to repeat my questions if any of them are not clear. However, they are not alternative; they all have to be answered.