I don't think there is a "trigger" other than just being available. It is **possible** (not sure of the likelihood) that in at least some locations I've been seen by them often enough to be identified not as "a" person but as "that" person and, through long observation, they've decided closer approach to me might be less risky than it would be with an unknown, or known/problem, person. Perhaps that is a trigger of a vague sort. The alternative is that what happens to me is happening to lots of people, they're just not paying attention, not noticing. That's possible ... an awful lot of people are just plain oblivious ... condition 0 or condition white ... mentally checked-out.
I'm not doing anything deliberate to entice a response, just making myself available by going where I think they are most likely to be, then doing what I do when I get there: hunt, fish, backpack, camp, explore, look for wildflowers, etc.
I guess with one exception. One time camping with "my research group", which seems to be once every couple years, we were messing around drumming, playing guitars, flutes, etc and things got "heavy". No screams, roars, knocks, or anything like that, but at one point, it felt like being inside a balloon that was being compressed. Firelight didn't go as far out into the dark even though the fire hadn't changed. Heavy, ominous vibe, etc. That didn't seem a reasonable or predictable outcome of the quite light-hearted action we were engaged in.
MIB