Exactly! For a sweaty gamer note: completing the last objective vastly ramps up the number of enemy patrols by almost 4x. Also sitting on the extract point causes more patrols to spawn, as does splitting up into separate groups.

So the absolute worst thing you can do to farm samples is complete the objectives, then have someone wait at extract while someone else goes and farms more samples. If you want to easily farm samples, save the last objective until after you've gathered your samples!