Using an SQL index over DDS file?

I created an index in our test environment to support a SELECT DISTINCT
query. The file has 4 milion rows in test, and 8 million rows in production.
The file is DDS-defined.

The index is in test, but Visual Explain says a table scan will be
performed, with the reason "No indexes exist". The query asks for the same
columns as the index, and in the same order. DSPDBR reports the index is
associated with the base file. I'm using the iNav "Run SQL Scripts".

Here is the index and query:
create index prod_mod.iml10026 on prod_mod.imp1001 (i1azcd asc, i1date asc,
i1time asc, i1badt asc);
select distinct i1azcd as location, i1date as observationdate, i1time as
observationtime, i1badt as costdate from prod_mod.imp1001;

The query will be utilized in embedded SQL in an RPGLE program.

Is there anything I can do to influeunce how the query performs, to say "use
this index"? This would be similar to SQL Server "hints". Is this a CQE vs.
SQE issue? Are there any gotchas between running the query in Run SQL
Scripts versus an embedded SQLRPGLE, other than naming convention and
date/time formats?
All is on V5R4.

Thanks,
Loyd