How do danger levels work?

right now most of my mob zones are at danger level 10, which is very high. the interesting thing is that this value does not change with the density of the mobs or even with how tough they are.

it looks like no matter what i do, the danger remains at around 10 … except for cases where my players simply overrun the zone, then it drops to 3 ore something like that.

i find this somewhat confusing