Question about Shroud's innate power

The one that pushes explorers and Dahan.

It's been my understanding that an innate power like this one is a single action targeting a single land. That would mean every piece moved by each threshold met would have to come from the same land.

It would seem that investing in those thresholds is a weak choice, since it's only useful if you happen to have several explorers and Dahan clustered in one land and want to move them all at once. That's a pretty niche scenario for the time it takes to gather all the elements.

Thematically it feels like these thresholds should be separate actions, so you can trigger your presence movement and effectively prevent builds.

Is that how it's supposed to work? Or is my original interpretation correct?

Thanks!