The election threshold is determined, based on (a) the number of seats to be filled; and (b) the number of votes cast.  It is the smallest number of votes that prohibits the election of more candidates than there are seats, or any number higher than 1 / (# of seats + 1).

As examples, the threshold for winning one seat in a three seat district is just over one-fourth of the votes; in a four seat district, just over one-fifth of the votes; and so on.