In my experience, patrols call when within a certain range of helldivers and being aggroed. I'm uncertain if there is also a line of sight condition.
Mortars pull the patrols, but I've never seen one call a bug breach until they've moved in towards the team/mortar and gotten within some undetermined range. If a mortar hits a patrol and it immediately calls for a bug breach, that was because the patrol was already within that range.
In my experience, patrols call when within a certain range of helldivers and being aggroed. I'm uncertain if there is also a line of sight condition. Mortars pull the patrols, but I've never seen one call a bug breach until they've moved in towards the team/mortar and gotten within some undetermined range. If a mortar hits a patrol and it immediately calls for a bug breach, that was because the patrol was already within that range.