"Abilities have a minimum range of 1 by default, but may have a higher minimum range (range 2-4, for example, meaning adjacent characters or spaces cannot be targeted)" - p16.
So a ability with range 4 has a minimum range of 1 and thus can affect anything within 4, not just units that are exactly four spaces away. Abilities with a specified range (like 2-3) are limited to that range.
There's at least one case where there's a specified range of 1-X (the Homonculus' flesh whip is range 1-2, there may be others that I missed), but range 1-2 should be functionally the same as range 2. I assume this is just a formatting inconsistency.