The BT sense is a DOOMS ability, the same quality that Sam and others carry, the attunement to the beach that the Stranding made possible in certain people. Amelie sensing BTs to great effect is the game noting that her connection to the other side is not merely cosmological but practical — she can navigate the boundary, read the presence of the dead in the living world, operate in the space between in ways that most people cannot.

The great effect qualifier is the sentence that contains the most information. Sam senses BTs. Amelie senses them to great effect. The difference in degree is the difference in kind — she is not sensitive to the beach the way a DOOMS carrier is sensitive to it. She is the beach wearing a person's face, sensing herself in every BT encounter, recognizing what she is through what she can perceive.