the only things we've done with zombies is increased their view distance so you don't stand 3 blocks next to a wandering horde waving your arms trying to get them to see you so you can take them on. we've done nothing to sleepers and stealth itself. the sleepers that appear in buildings are how they were set up from whoever made the poi's.. and in most cases have 10x the potential spawns than what actually does spawn.
does this make looting a little more dangerous? sure, welcome to ravenhearst where the zombies actually see you.
crouch before you trigger the sleeper volumes, sometimes it helps.
if you're in sunlight it doesn't do much good... what are you hiding in if you're in full view?
in a16 vanilla or modded (even in ravenhearst) night time is still a huge detriment to zombie sight. very easy currently to side step zombies in the dark and lose them as long as you're not shining a light on their faces. i doubt it will stay this way in a17 once they get all the senses working again.
just because it's interesting, these are taken from one of madmole's preview videos, this is what sleeper volumes look like in placement, you don't get all of them, it's random. lay them on thicker if there's an area you want to make sure has a few opportunities for zombies to be in.
so yes they have all kinds of positions, and they aren't aimed specifically at one entrance or another. a good sleeper volume will ensure that someone one sneaking in through a back window or side entrance isn't a cake walk.