The High_Non_Group index type may also be appropriate for a Low_Fast column.
It is almost always best to use an LF index if the number of unique values is low (less than 1,000). Consider this index first, if the column appears in the WHERE clause. Only when the number of unique values is high should other indexes (HG and HNG) be considered. For range queries with a high number of unique values, also consider having an HNG index.