Here is a little context. This is store_book_02 as seen in the POI editor. The blue areas are Sleeper Volumes (you can see the little sleeping zombies in them). The roof has three different volumes, and the rear loading dock has a single volume. There are various volumes inside the building.
View attachment 21877
This is a look at the first volume you'll encounter if you go in the Crack-A-Cafe door. The Sleeper Volume Trigger option can be "Passive", "Active", or "Attack". These settings correspond to SleeperVolumeFlag settings (in XML) of 1, 0, and 2 respectively. For this POI it looks like this:
<property name="SleeperVolumeFlags" value="0,0,2,0,0,2,2,2,1,1,2,2,2,2" />
That reads "
Active,
Active,
Attack,
Active,
Active,
Attack,
Attack,
Attack,
Passive,
Passive,
Attack,
Attack,
Attack"
You can see the glowing X-ray shapes of the sleeper positions behind the counter.
View attachment 21878
This is the same view for one of the rooftop volumes. This one is set to Attack ("2").
View attachment 21879
If you playtest this POI, you can sneak right up to the "Active" sleepers in the Cafe area, but as soon as you cross the border of the rooftop area set to "Attack", the Z's wake up and shamble towards you.
I checked out army_camp_01, which has this set of flags:
<property name="SleeperVolumeFlags" value="0,1,1,1,1,1" />
"
Active,
Passive,
Passive,
Passive,
Passive,
Passive,"
It looks like this. The big green volume encompassing the entire camp is the Active volume; the buildings and huts are Passive.
View attachment 21880
I playtested this POI and couldn't discern any difference between Active and Passive. I could sneak around in any of the volumes, but if I made noise the zombies would wake up and come after me. There's more going on here, but I don't have time at the moment to dig deeper.
Edit to add: one idea might be that Passive volumes are used in POI designs like above so you can have one big area (the whole camp) spawn in zombies and activate them if you make noise while also having smaller volumes within the bigger one which remain quiet/sleeping in spite of the hubub going on outside. Without this idea, the POI designer would have to use elite Tetris skills to craft a bunch of volumes for the outside areas which cover everything but don't intersect the huts.
The volumes marked "Attack" do seem to have clear behavior - as soon as you cross the boundary, all of the sleepers wake up and attack. Which is the root of OP's complaint I think.