Manual kei formula jinxed?

In the absence of wordtracker i’m doing some manual keyword effectiveness index research with two phrases:
Coffee machines - 60500 monthly search, 7310000 number of competitors

rent espresso coffee machines - 22 monthly search, 147000 competitors.

Now the KEI result puzzles me. I know intuitively phrase “Coffee machines” is far more competive than “rent espresso coffee machines” but the KEI scores say otherwise.

Have I miss calculated something? Or have I revealed the weakness of KEI as a too for guaging keyphrase competitiveness.

*The formula Ive used is number of searches to the power of 2 divided by
number of competitors.

Any insights welcome :slight_smile: