why 's%' use index '%s' doesn't?

When I use like operator, I found that search by 's%' is so much different from '%s'. Why is that and how to resolve this? Any help is appreciated(no CBO please). Thanks.

SQL> select * from table_name where name like 'tran%'; Execution Plan

   0 SELECT STATEMENT Optimizer=CHOOSE    1 0 TABLE ACCESS (BY INDEX ROWID) OF 'TABLE_NAME'    2 1 INDEX (RANGE SCAN) OF 'IN_SEQ_NAME' (NON-UNIQUE) SQL> select * from t where name like '%ion'; Execution Plan

   0 SELECT STATEMENT Optimizer=CHOOSE    1 0 TABLE ACCESS (FULL) OF 'TABLE_NAME' Received on Fri Jul 27 2001 - 00:10:03 CDT