Set PCT_FREE on IOT table in version 12c

Hi all,

I run the below DDL statement to set PCT_FREE to 5 for some IOT tables in oracle version 12c:

alter table SYS_IOT_OVER_92129 MOVE PCTFREE 5;

But received the below error:

SQL Error: ORA-25191: cannot reference overflow table of an index-organized table

25191. 00000 -  "cannot reference overflow table of an index-organized table"

*Cause:    An attempt to directly access the overflow table of an

           index-organized table

*Action:   Issue the statement against the parent index-organized table

           containing the specified overflow table.

I also found the IOT name for this table from all_tables. But their's PCT_FREE is zero (0). I know that the default value of PCT_FREE is 10, but don't understand why is the value of IOT name is zero. Are there problems if I set PCT_FREE of these IOT name tables to 5?