I've been having trouble finding an authoritative definition of the efficiency gap when more than 2 parties are involved. Ballotopedia points to an article by Nicholas Stephanopoulos and Eric McGhee, citing that "any vote for a losing candidate is wasted by definition, but so too is any vote beyond the 50 percent threshold needed (in a two-candidate race) to win a seat." Intuitively, I imagine many more votes are wasted when cast for the winning party if the result is a landslide (so the second-place candidate receives a tiny fraction of the votes), or when there are more than 2 candidates competing.
What happens to the measure in elections with more than 2 candidates? The "50 percent threshold" feels a little silly if the winner receives well below half of the votes. Is it as simple as saying that no votes for the winning party are wasted if they receive less than half of the votes?