Bids don't make sense, Amazon always uses my highest, what should I do?

In Amazon ads, I bid:

1.01 usd for "Science Fiction" phrase

0.91 usd for "hard science fiction" phrase

And in "customer search terms", somebody actually searched for "hard science fiction", but Amazon actually used my "Science Fiction" - 1.01 bid and it won. That person clicked.

I get that Amazon is trying to make money but still... I have zero impressions of hard science fiction phrase and exact. What's even the point of using longer and cheaper versions if my higher bid is gonna win everytime?

Should I just erase the science fiction phrase and use only exact for that alone?