WHERE Clause Tuning - Relational Operator for VARCHAR

My current customer has migrated from MS SQLServer to SQLAnywhere16.

In a legacy query they've used a relational operator against a VARCHAR20 column in the WHERE.

orders.order_status < 'N'

What was acceptable performance with MSSQLServer now has an undesirable delay in returning the rs under SQLAny16.

The SELECT has a 5-table join, but the performance is fine using the same query but with the one difference in using equality rather than the relational operator.

The scope of the distinct values within the column are all uppercase, no mixed sequences.

There is already a non-unique index for the column.

Any advice for tuning the performance, especially under-the-SQLAny-hood configuration is certainly welcome.

Thank you.