Hi,
I assume you are reffering to this option under the search instance settings? What that does is when set to 3 is, when a phrase is entered, say “3 5 666” it is considered as “666”. So 3 and 5 are ignored. If there is nothing left, then the an empty phrase search is executed.
There is a separate keyword lenght option on the index table settings here: https://i.imgur.com/fvKZCnG.png
I suggest setting that instead, so shorter keywords are not indexed whatsoever. After changing the option you will have to make a new index.
On top of that, I recommend setting the minimum character count to 3 so the search doesn’t trigger under 3 characters, just to make it more user friendly: https://i.imgur.com/TcdLEd0.png
This configuration will ensure that no entries below 3 characters are triggered, and for longer entries phrases below 3 characters are completely ignored (as they aren’t in the index)