I'm struggling to see which way around the cause and effect are, that lead to this part of ch4:

No one had ever come within the Kellynch circle, who could bear a comparison with Frederick Wentworth, as he stood in her memory.

Near the beginning of the chapter, it looks like the attachment was caused by Anne's and Captain Wentworth's individual personal advantages.

He was, at that time, a remarkably fine young man, with a great deal of intelligence, spirit and brilliancy; ... the encounter of such lavish recommendations could not fail.

On the other hand, near the end of the chapter, Anne seems to subscribe to the 'fix your affections on someone, and stop eyeing the alternatives' school of thought.

...how eloquent, at least, were her wishes on the side of early warm attachment, and a cheerful confidence in futurity, against that over-anxious caution which seems to insult exertion and distrust Providence!

I suppose it's also possible that there's a bit of both: she thinks highly of him, and so becomes attached, and so starts thinking even more highly of him.

Have any of you spotted any other indications? Or has JA left it open, for readers to believe as they choose?