Thank you! Every new big feature is a bit scary. I hope it is a good addition to the game.
That sleeping guard is not supposed to wake up when you walk close to it. I think I know what the problem is. There was a bug where if you got too close to an awake guard, the guard would not be able to catch the player. In shadows, an unaware guard could also walk very close past the player without noticing the player. Which seems unlikely, if the player is right next to the guard.
So I added a "red zone" to every guard. When the player gets too close to a guard, it triggers an instant alert. And if the player gets too close to an alerted guard, it triggers an instant catch. Though this "red zone" should not be active for sleeping guards, that's a bug. I'll fix it, thank you for letting me know ^^