HZD - Ultra-hard the spotting range is quite uneven - took out 1 of the 3 camps by the Ring of Metal (Revenge of the Nora) okay, along with the Camp Alarm. Started shooting the (green) barrels of Blaze & that alerted several distant Corrupted Scrappers that didn't show up on my 'radar' while scouting the camp. Those Scrappers summoned more that came in behind me out of nowhere and I died... One note - on the PC, there are only 3 outside bandit camps, but on the PS4 there are 4 outside camps. I'm dreading entering the Ring of Metal and trying to do that in stealth mode because of the weird spotting differences in Ultra-Hard.
Sometimes you get spotted by just 1 bandit which will show a yellow ? mark but you can hide & take out with a silent kill. However, it has to be a stealth kill out of sight of the others or they go high alert with a Red ? mark which can trigger the whole camp. A corrupted Watcher spotting you (Red ? mark) will alert the other Watchers and bandits - trigger the whole camp.
You can be next to a bandit in stealth in grass but still alert one on the far side of the camp somehow... not very even. I reloaded from last save quite a few times to see if I could spot any consistency in this but it's just not very even. Stealth head shots seem to be fairly consistent as long as the body isn't discovered by one of the bandits moving around.
Never had this difficulty in stealth mode with other lower difficulty levels often taking out a most of a bandit camp one by one in stealth mode.