Parliamentary Voting System and Constituencies Bill

The Deputy Leader of the House has supported the Government line that a constituency with 22,000 electors and three islands is treated as an exception. Argyll and Bute has 13 islands and a public ferry service, and covers a land area of about 5,000 square kilometres, with an electorate of 67,000. If the benchmark is three islands and 22,000 electors, why is there not an exception for other constituencies with islands—13 islands?