The large size of districts under STV are sometimes seen as presenting obstacle but in cities, a mayor reprsnted a whole city. if one person can do the work of representing a whole city, then why not 8 or 12 or 16? In Canada a typical single-member riding in the provinces is 16,000 sq. kms. with many much larger than that. 13 Canadian ridings are each larger than four times the size of the Scottish Highlands
The Highlands are represented by one UK MP by the way -- a single member is expected to represent all that area. if one person can represent that much territory, then surely 15 can represent the area between them.
Vast districts are not a problem judging by the size of single-member ridings in use now.
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is STV fair?
if a party does not nominate enough candidates under any system, the party will be shortchanged. under STV, each party knows they will take only the same share of seats as their share of votes so based on that expectation, they narrow their nomination to only what they expect plus one or two more in a typical district. if a party does much better than they expect, they can lose out. But that scientific forecast of seats won is possible only because STV is scientific. Under FPTP, every major party runs a candidate for every seat, hoping to get one of those lucky breaks that happens randomly.
BUT - the use of ranked votes means a party does not suffer if it over-nominates. In Malta both main parties nominate as many as twice the seats in the district. But in first count, you can pretty well see how many seats each of those parties will take in the end.. It then becomes two separate contests to see which candidate of the party is more generally popular, to take the party's seats in the district tht have not been won in the first count.
Comparing party seat share taken to first-preference vote share overlooks the benefit of ranked votes. That is - if a voter likes a smal party he or she has liberty to vote for whom they truly support (no strategic voting). If that small party does not take a seat in the district, the voter has consolation that their vote may be transferred to be used to elect someone of a larger party still favoured by the voter even if not his/her first choice. Those transfers skew the proportionality based on first-preference votes, as a party might take more votes later than their first-count share.