Not sure, I don't know the exact size of HH, but, like PL, they are of substantial size and have an acceptable amount of exploration to please people, to be coupled with the aforementioned system for special encounters as well.
I just tested this, it takes 59mins to FT from the Southern Passage to the Sorrows Camp, one minute less than it takes to get from The Mojave Outpost to Nipton. I think that makes HH about 1/20th of the size of the Mojave.
I really hope the developers aren't going to make a map broken up in 20 parts, accessed by loading screens with progress bars that look like something moving over a map, just to give some players the illusion of a really big map.
Or perhaps they could add just two extra nodes, completely white environments with nothing but a couple of signs marking the north and south poles, then it would be the biggest map ever.