In my experience Rampant sometimes switches to internal activities and wastes points on local migration. This is additionally provoked by factorio game engine: it generates far away chunks (3 chunks away from charted chunks border and 10 chunks away from player farthest visited chunks - the most distant point of these two is taken for chunk pre-generation area selection mechanism). It leads to effect that depending on map picture biters activities may sometimes (in over 50% cases or more!) target the areas you haven't even discovered yet. :-(
As I see it: If you don't have buildings 3-4 chunks away from biters nests they will prefer internal activities to sieging or raiding your infrastructure.
In my experience Rampant sometimes switches to internal activities and wastes points on local migration. This is additionally provoked by factorio game engine: it generates far away chunks (3 chunks away from charted chunks border and 10 chunks away from player farthest visited chunks - the most distant point of these two is taken for chunk pre-generation area selection mechanism). It leads to effect that depending on map picture biters activities may sometimes (in over 50% cases or more!) target the areas you haven't even discovered yet. :-(
As I see it: If you don't have buildings 3-4 chunks away from biters nests they will prefer internal activities to sieging or raiding your infrastructure.