Where was Blefuscu situated and what separated it from Lilliput?

At the beginning of chapter 5, part one, "Voyage of Lilliput", Gulliver states that Blefuscu is an island situated north east of Lilliput. Only a channel about 800 yards wide separate the two countries. In the book, Blefuscu are threatening to invade their neighbor so Gulliver states that "I avoided appearing on that side of the Coast, for fear of being discovered by some of the Enemy's Ships."
Blefuscu, "the other great Empire of the Universe," is Lilliput's sworn enemy. They have been at war with each other ever since the current king's grandfather changed the doctrine for opening an egg from the large end to the smaller end. Blefuscu used the uproar it caused to stir up trouble. They encouraged revolts within Lilliput and provided refuge for those that wanted to escape the country. The people of Blefuscu claim that opening an egg from the smaller end is "making a Schism in Religion, by offending against a fundamental Doctrine of our great Prophet."
In the third chapter Gulliver is asked to swear to a list of articles that includes the following 6th article.

He shall be our Ally against our enemies in the Island of Blefuscu, and do his utmost to destroy their Fleet, which is now preparing to invade Us.

In Gulliver's Travels the island nation of Blefuscu is situated in the South Indian Ocean. It sits to the northeast of its neighboring island and deadly enemy, Lilliput. The warring islands are separated by a narrow channel just 800 yards wide. It's a misfortune of geography that two such implacable foes should be so terribly close to each other.
Gulliver, as is his wont, gives us precise geographical locations for the places he visits. In the case of Blefuscu, its latitude is given as 30°2′S to the northwest of modern-day Tasmania in Australia. However, Blefuscu's location is geographically impossible because that precise location wouldn't have been an island at all but part of the great Australian landmass instead. But then, Australia was little explored when Swift wrote Gulliver's Travels, so not that much was known about this strange, exotic part of the world.