Stealth games are awesome. Glad our game can be categorized as such ^^
We will tweak the visual range for sure. The idea was to make it more challenging, but in the end it became almost not fun to play.
I didn't had time to make it visual, but there is a 2sec window. First the guard noticing you (the ? is shown) and then after 2 sec the guard will check if he can actually see you. If so, he will become alerted (!) and will hunt you - until he can't see you anymore.
So if you are quick enough you can possess them easily
And yes, the stair-shaped corridors are not fun to traverse ^^