substring index what is better way to query

Good morning,

I have an index I created on the prefix of a column:

create index location_geo_idx ON locations( substring(geohash, 0, 5));

I currently use a similar to query, but I wanted to know if there is a
faster way to query multiple value using this index than this?

select l.geohash from locations l where l.geohash similar to '(dr7g|dr7e)%';

My goal is to utilize 9 values each time for the geohash adjacent squares.

Best regards,

Ty