All memory always goes into *BASE. In order to have it allocated in another pool, you need to configure that pool to request memory from *BASE.
*MACHINE. *INTERACT and *SPOOL are shared pools that are pre-configured. You can modify their attributes. *BASE is also a shared pool, but the WRKSHRPOOL display shows that *BASE is different — there is no access to ‘Defined size’ attribute.
All other pools always allocate memory from *BASE and return memory back to *BASE.