Those are indeed the original sizes provided, and that 1" number does sound more like a bullet proof Sentry Box than a "fort!"
However, in the official expansion of the TSNS, fortifications are more practically sized: Fortresses are 13" to 18" along their sides, Forts are from 7" to 12", and Outposts are from 3" to 6". The time required to build each is also dependent on size'
There are now also Coastal Fortifications to consider.
Naturally, these have differing costs for Parliament and are a legitimate point of contention concerning policy and strategy during debates.
The rules now include specifics for such new Enemies of Empire as the Abyssinians, Ashanti, Afghans, Burmese, Chinese, Maori, and the Abor of the Northeast Frontier.
Full details of the greatly broadened 4th Edition of TSNS, now complete with large full color theater maps, printed map counters, Event Deck, record forms, and more, may be found here: link
I think you may be pleasantly amazed at what more players can do with "The Sun Never Sets!"
TVAG