For example, I fully expected to find some drowners or whatever at that lake near Fort St George, but it only turns out to be a prop.
The game managed to unsettle me even there, with just the water splash sounds.
This, and the area outside of Fort St. George (just before the exit "Western Path", I believe). The trail is lined with sight-line blocking hedgerows, with chances of multiple groups of savages lurking just above them in the slight inclines. Now, if the injuns had some kind of player tracking they would be more of a tangible threat when you're out of the ambush part of the battle.
I still think Fort Hope and Deep Forest maps were very tense, but that could just be my display setup. My monitor's already relatively dark, and only upping the color saturation left the game closer to its default state. This includes pitch-black shadows under the trees, and having to rely on silhouettes for enemies that are surprisingly good at blending in with the bushs' shapes.
One of the biggest "ohfuck" moments in my game was when I was stalking what I thought was another group of 2-3 savages in the Deep Forest. As I lined up one shithead for my musket shot, waiting for that gust of wind, I shot, missed (a bush's silhouette was moving right next to him so I thought that was his arm for a split second), and I heard the still-unsettling BOOM sound of "shit's popping off now" combat. No big deal, I thought, but then another 4 shitheads ignite themselves revealing their hitherto silent selves.
It could just be my rusty FPS skills, but dodging the otherwise trivial savages when there are 7 of them, including several that are just running straight up into your face to give you a-scalpin', is one of my best moments in the game.